1DBI(3) User Contributed Perl Documentation DBI(3)
2
6 DBI - Database independent interface for Perl
7
9 use DBI;
10 @driver_names = DBI->available_drivers;
12 %drivers = DBI->installed_drivers;
13 @data_sources = DBI->data_sources($driver_name, \%attr);
14 $dbh = DBI->connect($data_source, $username, $auth, \%attr);
16 $rv = $dbh->do($statement);
18 $rv = $dbh->do($statement, \%attr);
19 $rv = $dbh->do($statement, \%attr, @bind_values);
20 $ary_ref = $dbh->selectall_arrayref($statement);
22 $hash_ref = $dbh->selectall_hashref($statement, $key_field);
23 $ary_ref = $dbh->selectcol_arrayref($statement);
25 $ary_ref = $dbh->selectcol_arrayref($statement, \%attr);
26 @row_ary = $dbh->selectrow_array($statement);
28 $ary_ref = $dbh->selectrow_arrayref($statement);
29 $hash_ref = $dbh->selectrow_hashref($statement);
30 $sth = $dbh->prepare($statement);
32 $sth = $dbh->prepare_cached($statement);
33 $rc = $sth->bind_param($p_num, $bind_value);
35 $rc = $sth->bind_param($p_num, $bind_value, $bind_type);
36 $rc = $sth->bind_param($p_num, $bind_value, \%attr);
37 $rv = $sth->execute;
39 $rv = $sth->execute(@bind_values);
40 $rv = $sth->execute_array(\%attr, ...);
41 $rc = $sth->bind_col($col_num, \$col_variable);
43 $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
44 @row_ary = $sth->fetchrow_array;
46 $ary_ref = $sth->fetchrow_arrayref;
47 $hash_ref = $sth->fetchrow_hashref;
48 $ary_ref = $sth->fetchall_arrayref;
50 $ary_ref = $sth->fetchall_arrayref( $slice, $max_rows );
51 $hash_ref = $sth->fetchall_hashref( $key_field );
53 $rv = $sth->rows;
55 $rc = $dbh->begin_work;
57 $rc = $dbh->commit;
58 $rc = $dbh->rollback;
59 $quoted_string = $dbh->quote($string);
61 $rc = $h->err;
63 $str = $h->errstr;
64 $rv = $h->state;
65 $rc = $dbh->disconnect;
67 The synopsis above only lists the major methods and parameters.
69 GETTING HELP
71 General
72 Before asking any questions, reread this document, consult the archives
74 and read the DBI FAQ. The archives are listed at the end of this
75 document and on the DBI home page <http://dbi.perl.org/support/>
76 You might also like to read the Advanced DBI Tutorial at
78 <http://www.slideshare.net/Tim.Bunce/dbi-advanced-tutorial-2007>
79 To help you make the best use of the dbi-users mailing list, and any
81 other lists or forums you may use, I recommend that you read "Getting
82 Answers" by Mike Ash: <http://mikeash.com/getting_answers.html>.
83 Mailing Lists
85 If you have questions about DBI, or DBD driver modules, you can get
87 help from the dbi-users@perl.org mailing list. This is the best way to
88 get help. You don't have to subscribe to the list in order to post,
89 though I'd recommend it. You can get help on subscribing and using the
90 list by emailing dbi-users-help@perl.org.
91 Please note that Tim Bunce does not maintain the mailing lists or the
93 web pages (generous volunteers do that). So please don't send mail
94 directly to him; he just doesn't have the time to answer questions
95 personally. The dbi-users mailing list has lots of experienced people
96 who should be able to help you if you need it. If you do email Tim he
97 is very likely to just forward it to the mailing list.
98 IRC
100 DBI IRC Channel: #dbi on irc.perl.org (<irc://irc.perl.org/#dbi>)
102 Online
104 StackOverflow has a DBI tag
106 <http://stackoverflow.com/questions/tagged/dbi> with over 800
107 questions.
108 The DBI home page at <http://dbi.perl.org/> and the DBI FAQ at
110 <http://faq.dbi-support.com/> may be worth a visit. They include links
111 to other resources, but are rather out-dated.
112 Reporting a Bug
114 If you think you've found a bug then please read "How to Report Bugs
116 Effectively" by Simon Tatham:
117 <http://www.chiark.greenend.org.uk/~sgtatham/bugs.html>.
118 If you think you've found a memory leak then read "Memory Leaks".
120 Your problem is most likely related to the specific DBD driver module
122 you're using. If that's the case then click on the 'Bugs' link on the
123 <http://metacpan.org> page for your driver. Only submit a bug report
124 against the DBI itself if you're sure that your issue isn't related to
125 the driver you're using.
126 NOTES
128 This is the DBI specification that corresponds to DBI version 1.642
129 (see DBI::Changes for details).
130 The DBI is evolving at a steady pace, so it's good to check that you
132 have the latest copy.
133 The significant user-visible changes in each release are documented in
135 the DBI::Changes module so you can read them by executing "perldoc
136 DBI::Changes".
137 Some DBI changes require changes in the drivers, but the drivers can
139 take some time to catch up. Newer versions of the DBI have added
140 features that may not yet be supported by the drivers you use. Talk to
141 the authors of your drivers if you need a new feature that is not yet
142 supported.
143 Features added after DBI 1.21 (February 2002) are marked in the text
145 with the version number of the DBI release they first appeared in.
146 Extensions to the DBI API often use the "DBIx::*" namespace. See
148 "Naming Conventions and Name Space". DBI extension modules can be found
149 at <https://metacpan.org/search?q=DBIx>. And all modules related to
150 the DBI can be found at <https://metacpan.org/search?q=DBI>.
151
153 The DBI is a database access module for the Perl programming language.
154 It defines a set of methods, variables, and conventions that provide a
155 consistent database interface, independent of the actual database being
156 used.
157 It is important to remember that the DBI is just an interface. The DBI
159 is a layer of "glue" between an application and one or more database
160 driver modules. It is the driver modules which do most of the real
161 work. The DBI provides a standard interface and framework for the
162 drivers to operate within.
163 This document often uses terms like references, objects, methods. If
165 you're not familiar with those terms then it would be a good idea to
166 read at least the following perl manuals first: perlreftut, perldsc,
167 perllol, and perlboot.
168 Architecture of a DBI Application
170 |<- Scope of DBI ->|
171 .-. .--------------. .-------------.
172 .-------. | |---| XYZ Driver |---| XYZ Engine |
173 | Perl | | | `--------------' `-------------'
174 | script| |A| |D| .--------------. .-------------.
175 | using |--|P|--|B|---|Oracle Driver |---|Oracle Engine|
176 | DBI | |I| |I| `--------------' `-------------'
177 | API | | |...
178 |methods| | |... Other drivers
179 `-------' | |...
180 `-'
181 The API, or Application Programming Interface, defines the call
183 interface and variables for Perl scripts to use. The API is implemented
184 by the Perl DBI extension.
185 The DBI "dispatches" the method calls to the appropriate driver for
187 actual execution. The DBI is also responsible for the dynamic loading
188 of drivers, error checking and handling, providing default
189 implementations for methods, and many other non-database specific
190 duties.
191 Each driver contains implementations of the DBI methods using the
193 private interface functions of the corresponding database engine. Only
194 authors of sophisticated/multi-database applications or generic library
195 functions need be concerned with drivers.
196 Notation and Conventions
198 The following conventions are used in this document:
199 $dbh Database handle object
201 $sth Statement handle object
202 $drh Driver handle object (rarely seen or used in applications)
203 $h Any of the handle types above ($dbh, $sth, or $drh)
204 $rc General Return Code (boolean: true=ok, false=error)
205 $rv General Return Value (typically an integer)
206 @ary List of values returned from the database, typically a row of data
207 $rows Number of rows processed (if available, else -1)
208 $fh A filehandle
209 undef NULL values are represented by undefined values in Perl
210 \%attr Reference to a hash of attribute values passed to methods
211 Note that Perl will automatically destroy database and statement handle
213 objects if all references to them are deleted.
214 Outline Usage
216 To use DBI, first you need to load the DBI module:
217 use DBI;
219 use strict;
220 (The "use strict;" isn't required but is strongly recommended.)
222 Then you need to "connect" to your data source and get a handle for
224 that connection:
225 $dbh = DBI->connect($dsn, $user, $password,
227 { RaiseError => 1, AutoCommit => 0 });
228 Since connecting can be expensive, you generally just connect at the
230 start of your program and disconnect at the end.
231 Explicitly defining the required "AutoCommit" behaviour is strongly
233 recommended and may become mandatory in a later version. This
234 determines whether changes are automatically committed to the database
235 when executed, or need to be explicitly committed later.
236 The DBI allows an application to "prepare" statements for later
238 execution. A prepared statement is identified by a statement handle
239 held in a Perl variable. We'll call the Perl variable $sth in our
240 examples.
241 The typical method call sequence for a "SELECT" statement is:
243 prepare,
245 execute, fetch, fetch, ...
246 execute, fetch, fetch, ...
247 execute, fetch, fetch, ...
248 for example:
250 $sth = $dbh->prepare("SELECT foo, bar FROM table WHERE baz=?");
252 $sth->execute( $baz );
254 while ( @row = $sth->fetchrow_array ) {
256 print "@row\n";
257 }
258 The typical method call sequence for a non-"SELECT" statement is:
260 prepare,
262 execute,
263 execute,
264 execute.
265 for example:
267 $sth = $dbh->prepare("INSERT INTO table(foo,bar,baz) VALUES (?,?,?)");
269 while(<CSV>) {
271 chomp;
272 my ($foo,$bar,$baz) = split /,/;
273 $sth->execute( $foo, $bar, $baz );
274 }
275 The "do()" method can be used for non repeated non-"SELECT" statement
277 (or with drivers that don't support placeholders):
278 $rows_affected = $dbh->do("UPDATE your_table SET foo = foo + 1");
280 To commit your changes to the database (when "AutoCommit" is off):
282 $dbh->commit; # or call $dbh->rollback; to undo changes
284 Finally, when you have finished working with the data source, you
286 should "disconnect" from it:
287 $dbh->disconnect;
289 General Interface Rules & Caveats
291 The DBI does not have a concept of a "current session". Every session
292 has a handle object (i.e., a $dbh) returned from the "connect" method.
293 That handle object is used to invoke database related methods.
294 Most data is returned to the Perl script as strings. (Null values are
296 returned as "undef".) This allows arbitrary precision numeric data to
297 be handled without loss of accuracy. Beware that Perl may not preserve
298 the same accuracy when the string is used as a number.
299 Dates and times are returned as character strings in the current
301 default format of the corresponding database engine. Time zone effects
302 are database/driver dependent.
303 Perl supports binary data in Perl strings, and the DBI will pass binary
305 data to and from the driver without change. It is up to the driver
306 implementors to decide how they wish to handle such binary data.
307 Perl supports two kinds of strings: Unicode (utf8 internally) and non-
309 Unicode (defaults to iso-8859-1 if forced to assume an encoding).
310 Drivers should accept both kinds of strings and, if required, convert
311 them to the character set of the database being used. Similarly, when
312 fetching from the database character data that isn't iso-8859-1 the
313 driver should convert it into utf8.
314 Multiple SQL statements may not be combined in a single statement
316 handle ($sth), although some databases and drivers do support this
317 (notably Sybase and SQL Server).
318 Non-sequential record reads are not supported in this version of the
320 DBI. In other words, records can only be fetched in the order that the
321 database returned them, and once fetched they are forgotten.
322 Positioned updates and deletes are not directly supported by the DBI.
324 See the description of the "CursorName" attribute for an alternative.
325 Individual driver implementors are free to provide any private
327 functions and/or handle attributes that they feel are useful. Private
328 driver functions can be invoked using the DBI "func()" method. Private
329 driver attributes are accessed just like standard attributes.
330 Many methods have an optional "\%attr" parameter which can be used to
332 pass information to the driver implementing the method. Except where
333 specifically documented, the "\%attr" parameter can only be used to
334 pass driver specific hints. In general, you can ignore "\%attr"
335 parameters or pass it as "undef".
336 Naming Conventions and Name Space
338 The DBI package and all packages below it ("DBI::*") are reserved for
339 use by the DBI. Extensions and related modules use the "DBIx::"
340 namespace (see <http://www.perl.com/CPAN/modules/by-module/DBIx/>).
341 Package names beginning with "DBD::" are reserved for use by DBI
342 database drivers. All environment variables used by the DBI or by
343 individual DBDs begin with ""DBI_"" or ""DBD_"".
344 The letter case used for attribute names is significant and plays an
346 important part in the portability of DBI scripts. The case of the
347 attribute name is used to signify who defined the meaning of that name
348 and its values.
349 Case of name Has a meaning defined by
351 ------------ ------------------------
352 UPPER_CASE Standards, e.g., X/Open, ISO SQL92 etc (portable)
353 MixedCase DBI API (portable), underscores are not used.
354 lower_case Driver or database engine specific (non-portable)
355 It is of the utmost importance that Driver developers only use
357 lowercase attribute names when defining private attributes. Private
358 attribute names must be prefixed with the driver name or suitable
359 abbreviation (e.g., ""ora_"" for Oracle, ""ing_"" for Ingres, etc).
360 SQL - A Query Language
362 Most DBI drivers require applications to use a dialect of SQL
363 (Structured Query Language) to interact with the database engine. The
364 "Standards Reference Information" section provides links to useful
365 information about SQL.
366 The DBI itself does not mandate or require any particular language to
368 be used; it is language independent. In ODBC terms, the DBI is in
369 "pass-thru" mode, although individual drivers might not be. The only
370 requirement is that queries and other statements must be expressed as a
371 single string of characters passed as the first argument to the
372 "prepare" or "do" methods.
373 For an interesting diversion on the real history of RDBMS and SQL, from
375 the people who made it happen, see:
376 http://www.mcjones.org/System_R/SQL_Reunion_95/sqlr95.html
378 Follow the "Full Contents" then "Intergalactic dataspeak" links for the
380 SQL history.
381 Placeholders and Bind Values
383 Some drivers support placeholders and bind values. Placeholders, also
384 called parameter markers, are used to indicate values in a database
385 statement that will be supplied later, before the prepared statement is
386 executed. For example, an application might use the following to
387 insert a row of data into the SALES table:
388 INSERT INTO sales (product_code, qty, price) VALUES (?, ?, ?)
390 or the following, to select the description for a product:
392 SELECT description FROM products WHERE product_code = ?
394 The "?" characters are the placeholders. The association of actual
396 values with placeholders is known as binding, and the values are
397 referred to as bind values. Note that the "?" is not enclosed in
398 quotation marks, even when the placeholder represents a string.
399 Some drivers also allow placeholders like ":"name and ":"N (e.g., ":1",
401 ":2", and so on) in addition to "?", but their use is not portable.
402 If the ":"N form of placeholder is supported by the driver you're
404 using, then you should be able to use either "bind_param" or "execute"
405 to bind values. Check your driver documentation.
406 Some drivers allow you to prevent the recognition of a placeholder by
408 placing a single backslash character ("\") immediately before it. The
409 driver will remove the backslash character and ignore the placeholder,
410 passing it unchanged to the backend. If the driver supports this then
411 "get_info"(9000) will return true.
412 With most drivers, placeholders can't be used for any element of a
414 statement that would prevent the database server from validating the
415 statement and creating a query execution plan for it. For example:
416 "SELECT name, age FROM ?" # wrong (will probably fail)
418 "SELECT name, ? FROM people" # wrong (but may not 'fail')
419 Also, placeholders can only represent single scalar values. For
421 example, the following statement won't work as expected for more than
422 one value:
423 "SELECT name, age FROM people WHERE name IN (?)" # wrong
425 "SELECT name, age FROM people WHERE name IN (?,?)" # two names
426 When using placeholders with the SQL "LIKE" qualifier, you must
428 remember that the placeholder substitutes for the whole string. So you
429 should use ""... LIKE ? ..."" and include any wildcard characters in
430 the value that you bind to the placeholder.
431 NULL Values
433 Undefined values, or "undef", are used to indicate NULL values. You
435 can insert and update columns with a NULL value as you would a non-NULL
436 value. These examples insert and update the column "age" with a NULL
437 value:
438 $sth = $dbh->prepare(qq{
440 INSERT INTO people (fullname, age) VALUES (?, ?)
441 });
442 $sth->execute("Joe Bloggs", undef);
443 $sth = $dbh->prepare(qq{
445 UPDATE people SET age = ? WHERE fullname = ?
446 });
447 $sth->execute(undef, "Joe Bloggs");
448 However, care must be taken when trying to use NULL values in a "WHERE"
450 clause. Consider:
451 SELECT fullname FROM people WHERE age = ?
453 Binding an "undef" (NULL) to the placeholder will not select rows which
455 have a NULL "age"! At least for database engines that conform to the
456 SQL standard. Refer to the SQL manual for your database engine or any
457 SQL book for the reasons for this. To explicitly select NULLs you have
458 to say ""WHERE age IS NULL"".
459 A common issue is to have a code fragment handle a value that could be
461 either "defined" or "undef" (non-NULL or NULL) at runtime. A simple
462 technique is to prepare the appropriate statement as needed, and
463 substitute the placeholder for non-NULL cases:
464 $sql_clause = defined $age? "age = ?" : "age IS NULL";
466 $sth = $dbh->prepare(qq{
467 SELECT fullname FROM people WHERE $sql_clause
468 });
469 $sth->execute(defined $age ? $age : ());
470 The following technique illustrates qualifying a "WHERE" clause with
472 several columns, whose associated values ("defined" or "undef") are in
473 a hash %h:
474 for my $col ("age", "phone", "email") {
476 if (defined $h{$col}) {
477 push @sql_qual, "$col = ?";
478 push @sql_bind, $h{$col};
479 }
480 else {
481 push @sql_qual, "$col IS NULL";
482 }
483 }
484 $sql_clause = join(" AND ", @sql_qual);
485 $sth = $dbh->prepare(qq{
486 SELECT fullname FROM people WHERE $sql_clause
487 });
488 $sth->execute(@sql_bind);
489 The techniques above call prepare for the SQL statement with each call
491 to execute. Because calls to prepare() can be expensive, performance
492 can suffer when an application iterates many times over statements like
493 the above.
494 A better solution is a single "WHERE" clause that supports both NULL
496 and non-NULL comparisons. Its SQL statement would need to be prepared
497 only once for all cases, thus improving performance. Several examples
498 of "WHERE" clauses that support this are presented below. But each
499 example lacks portability, robustness, or simplicity. Whether an
500 example is supported on your database engine depends on what SQL
501 extensions it provides, and where it supports the "?" placeholder in a
502 statement.
503 0) age = ?
505 1) NVL(age, xx) = NVL(?, xx)
506 2) ISNULL(age, xx) = ISNULL(?, xx)
507 3) DECODE(age, ?, 1, 0) = 1
508 4) age = ? OR (age IS NULL AND ? IS NULL)
509 5) age = ? OR (age IS NULL AND SP_ISNULL(?) = 1)
510 6) age = ? OR (age IS NULL AND ? = 1)
511 Statements formed with the above "WHERE" clauses require execute
513 statements as follows. The arguments are required, whether their
514 values are "defined" or "undef".
515 0,1,2,3) $sth->execute($age);
517 4,5) $sth->execute($age, $age);
518 6) $sth->execute($age, defined($age) ? 0 : 1);
519 Example 0 should not work (as mentioned earlier), but may work on a few
521 database engines anyway (e.g. Sybase). Example 0 is part of examples
522 4, 5, and 6, so if example 0 works, these other examples may work, even
523 if the engine does not properly support the right hand side of the "OR"
524 expression.
525 Examples 1 and 2 are not robust: they require that you provide a valid
527 column value xx (e.g. '~') which is not present in any row. That means
528 you must have some notion of what data won't be stored in the column,
529 and expect clients to adhere to that.
530 Example 5 requires that you provide a stored procedure (SP_ISNULL in
532 this example) that acts as a function: it checks whether a value is
533 null, and returns 1 if it is, or 0 if not.
534 Example 6, the least simple, is probably the most portable, i.e., it
536 should work with most, if not all, database engines.
537 Here is a table that indicates which examples above are known to work
539 on various database engines:
540 -----Examples------
542 0 1 2 3 4 5 6
543 - - - - - - -
544 Oracle 9 N Y N Y Y ? Y
545 Informix IDS 9 N N N Y N Y Y
546 MS SQL N N Y N Y ? Y
547 Sybase Y N N N N N Y
548 AnyData,DBM,CSV Y N N N Y Y* Y
549 SQLite 3.3 N N N N Y N N
550 MSAccess N N N N Y N Y
551 * Works only because Example 0 works.
553 DBI provides a sample perl script that will test the examples above on
555 your database engine and tell you which ones work. It is located in
556 the ex/ subdirectory of the DBI source distribution, or here:
557 <https://github.com/perl5-dbi/dbi/blob/master/ex/perl_dbi_nulls_test.pl>
558 Please use the script to help us fill-in and maintain this table.
559 Performance
561 Without using placeholders, the insert statement shown previously would
563 have to contain the literal values to be inserted and would have to be
564 re-prepared and re-executed for each row. With placeholders, the insert
565 statement only needs to be prepared once. The bind values for each row
566 can be given to the "execute" method each time it's called. By avoiding
567 the need to re-prepare the statement for each row, the application
568 typically runs many times faster. Here's an example:
569 my $sth = $dbh->prepare(q{
571 INSERT INTO sales (product_code, qty, price) VALUES (?, ?, ?)
572 }) or die $dbh->errstr;
573 while (<>) {
574 chomp;
575 my ($product_code, $qty, $price) = split /,/;
576 $sth->execute($product_code, $qty, $price) or die $dbh->errstr;
577 }
578 $dbh->commit or die $dbh->errstr;
579 See "execute" and "bind_param" for more details.
581 The "q{...}" style quoting used in this example avoids clashing with
583 quotes that may be used in the SQL statement. Use the double-quote like
584 "qq{...}" operator if you want to interpolate variables into the
585 string. See "Quote and Quote-like Operators" in perlop for more
586 details.
587 See also the "bind_columns" method, which is used to associate Perl
589 variables with the output columns of a "SELECT" statement.
590
592 In this section, we cover the DBI class methods, utility functions, and
593 the dynamic attributes associated with generic DBI handles.
594 DBI Constants
596 Constants representing the values of the SQL standard types can be
597 imported individually by name, or all together by importing the special
598 ":sql_types" tag.
599 The names and values of all the defined SQL standard types can be
601 produced like this:
602 foreach (@{ $DBI::EXPORT_TAGS{sql_types} }) {
604 printf "%s=%d\n", $_, &{"DBI::$_"};
605 }
606 These constants are defined by SQL/CLI, ODBC or both. "SQL_BIGINT" has
608 conflicting codes in SQL/CLI and ODBC, DBI uses the ODBC one.
609 See the "type_info", "type_info_all", and "bind_param" methods for
611 possible uses.
612 Note that just because the DBI defines a named constant for a given
614 data type doesn't mean that drivers will support that data type.
615 DBI Class Methods
617 The following methods are provided by the DBI class:
618 "parse_dsn"
620 ($scheme, $driver, $attr_string, $attr_hash, $driver_dsn) = DBI->parse_dsn($dsn)
622 or die "Can't parse DBI DSN '$dsn'";
623 Breaks apart a DBI Data Source Name (DSN) and returns the individual
625 parts. If $dsn doesn't contain a valid DSN then parse_dsn() returns an
626 empty list.
627 $scheme is the first part of the DSN and is currently always 'dbi'.
629 $driver is the driver name, possibly defaulted to $ENV{DBI_DRIVER}, and
630 may be undefined. $attr_string is the contents of the optional
631 attribute string, which may be undefined. If $attr_string is not empty
632 then $attr_hash is a reference to a hash containing the parsed
633 attribute names and values. $driver_dsn is the last part of the DBI
634 DSN string. For example:
635 ($scheme, $driver, $attr_string, $attr_hash, $driver_dsn)
637 = DBI->parse_dsn("dbi:MyDriver(RaiseError=>1):db=test;port=42");
638 $scheme = 'dbi';
639 $driver = 'MyDriver';
640 $attr_string = 'RaiseError=>1';
641 $attr_hash = { 'RaiseError' => '1' };
642 $driver_dsn = 'db=test;port=42';
643 The parse_dsn() method was added in DBI 1.43.
645 "connect"
647 $dbh = DBI->connect($data_source, $username, $password)
649 or die $DBI::errstr;
650 $dbh = DBI->connect($data_source, $username, $password, \%attr)
651 or die $DBI::errstr;
652 Establishes a database connection, or session, to the requested
654 $data_source. Returns a database handle object if the connection
655 succeeds. Use "$dbh->disconnect" to terminate the connection.
656 If the connect fails (see below), it returns "undef" and sets both
658 $DBI::err and $DBI::errstr. (It does not explicitly set $!.) You should
659 generally test the return status of "connect" and "print $DBI::errstr"
660 if it has failed.
661 Multiple simultaneous connections to multiple databases through
663 multiple drivers can be made via the DBI. Simply make one "connect"
664 call for each database and keep a copy of each returned database
665 handle.
666 The $data_source value must begin with ""dbi:"driver_name":"". The
668 driver_name specifies the driver that will be used to make the
669 connection. (Letter case is significant.)
670 As a convenience, if the $data_source parameter is undefined or empty,
672 the DBI will substitute the value of the environment variable
673 "DBI_DSN". If just the driver_name part is empty (i.e., the
674 $data_source prefix is ""dbi::""), the environment variable
675 "DBI_DRIVER" is used. If neither variable is set, then "connect" dies.
676 Examples of $data_source values are:
678 dbi:DriverName:database_name
680 dbi:DriverName:database_name@hostname:port
681 dbi:DriverName:database=database_name;host=hostname;port=port
682 There is no standard for the text following the driver name. Each
684 driver is free to use whatever syntax it wants. The only requirement
685 the DBI makes is that all the information is supplied in a single
686 string. You must consult the documentation for the drivers you are
687 using for a description of the syntax they require.
688 It is recommended that drivers support the ODBC style, shown in the
690 last example above. It is also recommended that they support the three
691 common names '"host"', '"port"', and '"database"' (plus '"db"' as an
692 alias for "database"). This simplifies automatic construction of basic
693 DSNs: "dbi:$driver:database=$db;host=$host;port=$port". Drivers should
694 aim to 'do something reasonable' when given a DSN in this form, but if
695 any part is meaningless for that driver (such as 'port' for Informix)
696 it should generate an error if that part is not empty.
697 If the environment variable "DBI_AUTOPROXY" is defined (and the driver
699 in $data_source is not ""Proxy"") then the connect request will
700 automatically be changed to:
701 $ENV{DBI_AUTOPROXY};dsn=$data_source
703 "DBI_AUTOPROXY" is typically set as
705 ""dbi:Proxy:hostname=...;port=..."". If $ENV{DBI_AUTOPROXY} doesn't
706 begin with '"dbi:"' then "dbi:Proxy:" will be prepended to it first.
707 See the DBD::Proxy documentation for more details.
708 If $username or $password are undefined (rather than just empty), then
710 the DBI will substitute the values of the "DBI_USER" and "DBI_PASS"
711 environment variables, respectively. The DBI will warn if the
712 environment variables are not defined. However, the everyday use of
713 these environment variables is not recommended for security reasons.
714 The mechanism is primarily intended to simplify testing. See below for
715 alternative way to specify the username and password.
716 "DBI->connect" automatically installs the driver if it has not been
718 installed yet. Driver installation either returns a valid driver
719 handle, or it dies with an error message that includes the string
720 ""install_driver"" and the underlying problem. So "DBI->connect" will
721 die on a driver installation failure and will only return "undef" on a
722 connect failure, in which case $DBI::errstr will hold the error
723 message. Use "eval" if you need to catch the ""install_driver"" error.
724 The $data_source argument (with the ""dbi:...:"" prefix removed) and
726 the $username and $password arguments are then passed to the driver for
727 processing. The DBI does not define any interpretation for the contents
728 of these fields. The driver is free to interpret the $data_source,
729 $username, and $password fields in any way, and supply whatever
730 defaults are appropriate for the engine being accessed. (Oracle, for
731 example, uses the ORACLE_SID and TWO_TASK environment variables if no
732 $data_source is specified.)
733 The "AutoCommit" and "PrintError" attributes for each connection
735 default to "on". (See "AutoCommit" and "PrintError" for more
736 information.) However, it is strongly recommended that you explicitly
737 define "AutoCommit" rather than rely on the default. The "PrintWarn"
738 attribute defaults to true.
739 The "\%attr" parameter can be used to alter the default settings of
741 "PrintError", "RaiseError", "AutoCommit", and other attributes. For
742 example:
743 $dbh = DBI->connect($data_source, $user, $pass, {
745 PrintError => 0,
746 AutoCommit => 0
747 });
748 The username and password can also be specified using the attributes
750 "Username" and "Password", in which case they take precedence over the
751 $username and $password parameters.
752 You can also define connection attribute values within the $data_source
754 parameter. For example:
755 dbi:DriverName(PrintWarn=>0,PrintError=>0,Taint=>1):...
757 Individual attributes values specified in this way take precedence over
759 any conflicting values specified via the "\%attr" parameter to
760 "connect".
761 The "dbi_connect_method" attribute can be used to specify which driver
763 method should be called to establish the connection. The only useful
764 values are 'connect', 'connect_cached', or some specialized case like
765 'Apache::DBI::connect' (which is automatically the default when running
766 within Apache).
767 Where possible, each session ($dbh) is independent from the
769 transactions in other sessions. This is useful when you need to hold
770 cursors open across transactions--for example, if you use one session
771 for your long lifespan cursors (typically read-only) and another for
772 your short update transactions.
773 For compatibility with old DBI scripts, the driver can be specified by
775 passing its name as the fourth argument to "connect" (instead of
776 "\%attr"):
777 $dbh = DBI->connect($data_source, $user, $pass, $driver);
779 In this "old-style" form of "connect", the $data_source should not
781 start with ""dbi:driver_name:"". (If it does, the embedded driver_name
782 will be ignored). Also note that in this older form of "connect", the
783 "$dbh->{AutoCommit}" attribute is undefined, the "$dbh->{PrintError}"
784 attribute is off, and the old "DBI_DBNAME" environment variable is
785 checked if "DBI_DSN" is not defined. Beware that this "old-style"
786 "connect" will soon be withdrawn in a future version of DBI.
787 "connect_cached"
789 $dbh = DBI->connect_cached($data_source, $username, $password)
791 or die $DBI::errstr;
792 $dbh = DBI->connect_cached($data_source, $username, $password, \%attr)
793 or die $DBI::errstr;
794 "connect_cached" is like "connect", except that the database handle
796 returned is also stored in a hash associated with the given parameters.
797 If another call is made to "connect_cached" with the same parameter
798 values, then the corresponding cached $dbh will be returned if it is
799 still valid. The cached database handle is replaced with a new
800 connection if it has been disconnected or if the "ping" method fails.
801 Note that the behaviour of this method differs in several respects from
803 the behaviour of persistent connections implemented by Apache::DBI.
804 However, if Apache::DBI is loaded then "connect_cached" will use it.
805 Caching connections can be useful in some applications, but it can also
807 cause problems, such as too many connections, and so should be used
808 with care. In particular, avoid changing the attributes of a database
809 handle created via connect_cached() because it will affect other code
810 that may be using the same handle. When connect_cached() returns a
811 handle the attributes will be reset to their initial values. This can
812 cause problems, especially with the "AutoCommit" attribute.
813 Also, to ensure that the attributes passed are always the same, avoid
815 passing references inline. For example, the "Callbacks" attribute is
816 specified as a hash reference. Be sure to declare it external to the
817 call to connect_cached(), such that the hash reference is not re-
818 created on every call. A package-level lexical works well:
819 package MyDBH;
821 my $cb = {
822 'connect_cached.reused' => sub { delete $_[4]->{AutoCommit} },
823 };
824 sub dbh {
826 DBI->connect_cached( $dsn, $username, $auth, { Callbacks => $cb });
827 }
828 Where multiple separate parts of a program are using connect_cached()
830 to connect to the same database with the same (initial) attributes it
831 is a good idea to add a private attribute to the connect_cached() call
832 to effectively limit the scope of the caching. For example:
833 DBI->connect_cached(..., { private_foo_cachekey => "Bar", ... });
835 Handles returned from that connect_cached() call will only be returned
837 by other connect_cached() call elsewhere in the code if those other
838 calls also pass in the same attribute values, including the private
839 one. (I've used "private_foo_cachekey" here as an example, you can use
840 any attribute name with a "private_" prefix.)
841 Taking that one step further, you can limit a particular
843 connect_cached() call to return handles unique to that one place in the
844 code by setting the private attribute to a unique value for that place:
845 DBI->connect_cached(..., { private_foo_cachekey => __FILE__.__LINE__, ... });
847 By using a private attribute you still get connection caching for the
849 individual calls to connect_cached() but, by making separate database
850 connections for separate parts of the code, the database handles are
851 isolated from any attribute changes made to other handles.
852 The cache can be accessed (and cleared) via the "CachedKids" attribute:
854 my $CachedKids_hashref = $dbh->{Driver}->{CachedKids};
856 %$CachedKids_hashref = () if $CachedKids_hashref;
857 "available_drivers"
859 @ary = DBI->available_drivers;
861 @ary = DBI->available_drivers($quiet);
862 Returns a list of all available drivers by searching for "DBD::*"
864 modules through the directories in @INC. By default, a warning is given
865 if some drivers are hidden by others of the same name in earlier
866 directories. Passing a true value for $quiet will inhibit the warning.
867 "installed_drivers"
869 %drivers = DBI->installed_drivers();
871 Returns a list of driver name and driver handle pairs for all drivers
873 'installed' (loaded) into the current process. The driver name does
874 not include the 'DBD::' prefix.
875 To get a list of all drivers available in your perl installation you
877 can use "available_drivers".
878 Added in DBI 1.49.
880 "installed_versions"
882 DBI->installed_versions;
884 @ary = DBI->installed_versions;
885 $hash = DBI->installed_versions;
886 Calls available_drivers() and attempts to load each of them in turn
888 using install_driver(). For each load that succeeds the driver name
889 and version number are added to a hash. When running under
890 DBI::PurePerl drivers which appear not be pure-perl are ignored.
891 When called in array context the list of successfully loaded drivers is
893 returned (without the 'DBD::' prefix).
894 When called in scalar context an extra entry for the "DBI" is added
896 (and "DBI::PurePerl" if appropriate) and a reference to the hash is
897 returned.
898 When called in a void context the installed_versions() method will
900 print out a formatted list of the hash contents, one per line, along
901 with some other information about the DBI version and OS.
902 Due to the potentially high memory cost and unknown risks of loading in
904 an unknown number of drivers that just happen to be installed on the
905 system, this method is not recommended for general use. Use
906 available_drivers() instead.
907 The installed_versions() method is primarily intended as a quick way to
909 see from the command line what's installed. For example:
910 perl -MDBI -e 'DBI->installed_versions'
912 The installed_versions() method was added in DBI 1.38.
914 "data_sources"
916 @ary = DBI->data_sources($driver);
918 @ary = DBI->data_sources($driver, \%attr);
919 Returns a list of data sources (databases) available via the named
921 driver. If $driver is empty or "undef", then the value of the
922 "DBI_DRIVER" environment variable is used.
923 The driver will be loaded if it hasn't been already. Note that if the
925 driver loading fails then data_sources() dies with an error message
926 that includes the string ""install_driver"" and the underlying problem.
927 Data sources are returned in a form suitable for passing to the
929 "connect" method (that is, they will include the ""dbi:$driver:""
930 prefix).
931 Note that many drivers have no way of knowing what data sources might
933 be available for it. These drivers return an empty or incomplete list
934 or may require driver-specific attributes.
935 There is also a data_sources() method defined for database handles.
937 "trace"
939 DBI->trace($trace_setting)
941 DBI->trace($trace_setting, $trace_filename)
942 DBI->trace($trace_setting, $trace_filehandle)
943 $trace_setting = DBI->trace;
944 The "DBI->trace" method sets the global default trace settings and
946 returns the previous trace settings. It can also be used to change
947 where the trace output is sent.
948 There's a similar method, "$h->trace", which sets the trace settings
950 for the specific handle it's called on.
951 See the "TRACING" section for full details about the DBI's powerful
953 tracing facilities.
954 "visit_handles"
956 DBI->visit_handles( $coderef );
958 DBI->visit_handles( $coderef, $info );
959 Where $coderef is a reference to a subroutine and $info is an arbitrary
961 value which, if undefined, defaults to a reference to an empty hash.
962 Returns $info.
963 For each installed driver handle, if any, $coderef is invoked as:
965 $coderef->($driver_handle, $info);
967 If the execution of $coderef returns a true value then
969 "visit_child_handles" is called on that child handle and passed the
970 returned value as $info.
971 For example:
973 my $info = $dbh->{Driver}->visit_child_handles(sub {
975 my ($h, $info) = @_;
976 ++$info->{ $h->{Type} }; # count types of handles (dr/db/st)
977 return $info; # visit kids
978 });
979 See also "visit_child_handles".
981 DBI Utility Functions
983 In addition to the DBI methods listed in the previous section, the DBI
984 package also provides several utility functions.
985 These can be imported into your code by listing them in the "use"
987 statement. For example:
988 use DBI qw(neat data_diff);
990 Alternatively, all these utility functions (except hash) can be
992 imported using the ":utils" import tag. For example:
993 use DBI qw(:utils);
995 "data_string_desc"
997 $description = data_string_desc($string);
999 Returns an informal description of the string. For example:
1001 UTF8 off, ASCII, 42 characters 42 bytes
1003 UTF8 off, non-ASCII, 42 characters 42 bytes
1004 UTF8 on, non-ASCII, 4 characters 6 bytes
1005 UTF8 on but INVALID encoding, non-ASCII, 4 characters 6 bytes
1006 UTF8 off, undef
1007 The initial "UTF8" on/off refers to Perl's internal SvUTF8 flag. If
1009 $string has the SvUTF8 flag set but the sequence of bytes it contains
1010 are not a valid UTF-8 encoding then data_string_desc() will report
1011 "UTF8 on but INVALID encoding".
1012 The "ASCII" vs "non-ASCII" portion shows "ASCII" if all the characters
1014 in the string are ASCII (have code points <= 127).
1015 The data_string_desc() function was added in DBI 1.46.
1017 "data_string_diff"
1019 $diff = data_string_diff($a, $b);
1021 Returns an informal description of the first character difference
1023 between the strings. If both $a and $b contain the same sequence of
1024 characters then data_string_diff() returns an empty string. For
1025 example:
1026 Params a & b Result
1028 ------------ ------
1029 'aaa', 'aaa' ''
1030 'aaa', 'abc' 'Strings differ at index 2: a[2]=a, b[2]=b'
1031 'aaa', undef 'String b is undef, string a has 3 characters'
1032 'aaa', 'aa' 'String b truncated after 2 characters'
1033 Unicode characters are reported in "\x{XXXX}" format. Unicode code
1035 points in the range U+0800 to U+08FF are unassigned and most likely to
1036 occur due to double-encoding. Characters in this range are reported as
1037 "\x{08XX}='C'" where "C" is the corresponding latin-1 character.
1038 The data_string_diff() function only considers logical characters and
1040 not the underlying encoding. See "data_diff" for an alternative.
1041 The data_string_diff() function was added in DBI 1.46.
1043 "data_diff"
1045 $diff = data_diff($a, $b);
1047 $diff = data_diff($a, $b, $logical);
1048 Returns an informal description of the difference between two strings.
1050 It calls "data_string_desc" and "data_string_diff" and returns the
1051 combined results as a multi-line string.
1052 For example, "data_diff("abc", "ab\x{263a}")" will return:
1054 a: UTF8 off, ASCII, 3 characters 3 bytes
1056 b: UTF8 on, non-ASCII, 3 characters 5 bytes
1057 Strings differ at index 2: a[2]=c, b[2]=\x{263A}
1058 If $a and $b are identical in both the characters they contain and
1060 their physical encoding then data_diff() returns an empty string. If
1061 $logical is true then physical encoding differences are ignored (but
1062 are still reported if there is a difference in the characters).
1063 The data_diff() function was added in DBI 1.46.
1065 "neat"
1067 $str = neat($value);
1069 $str = neat($value, $maxlen);
1070 Return a string containing a neat (and tidy) representation of the
1072 supplied value.
1073 Strings will be quoted, although internal quotes will not be escaped.
1075 Values known to be numeric will be unquoted. Undefined (NULL) values
1076 will be shown as "undef" (without quotes).
1077 If the string is flagged internally as utf8 then double quotes will be
1079 used, otherwise single quotes are used and unprintable characters will
1080 be replaced by dot (.).
1081 For result strings longer than $maxlen the result string will be
1083 truncated to "$maxlen-4" and ""...'"" will be appended. If $maxlen is
1084 0 or "undef", it defaults to $DBI::neat_maxlen which, in turn, defaults
1085 to 400.
1086 This function is designed to format values for human consumption. It
1088 is used internally by the DBI for "trace" output. It should typically
1089 not be used for formatting values for database use. (See also
1090 "quote".)
1091 "neat_list"
1093 $str = neat_list(\@listref, $maxlen, $field_sep);
1095 Calls "neat" on each element of the list and returns a string
1097 containing the results joined with $field_sep. $field_sep defaults to
1098 ", ".
1099 "looks_like_number"
1101 @bool = looks_like_number(@array);
1103 Returns true for each element that looks like a number. Returns false
1105 for each element that does not look like a number. Returns "undef" for
1106 each element that is undefined or empty.
1107 "hash"
1109 $hash_value = DBI::hash($buffer, $type);
1111 Return a 32-bit integer 'hash' value corresponding to the contents of
1113 $buffer. The $type parameter selects which kind of hash algorithm
1114 should be used.
1115 For the technically curious, type 0 (which is the default if $type
1117 isn't specified) is based on the Perl 5.1 hash except that the value is
1118 forced to be negative (for obscure historical reasons). Type 1 is the
1119 better "Fowler / Noll / Vo" (FNV) hash. See
1120 <http://www.isthe.com/chongo/tech/comp/fnv/> for more information.
1121 Both types are implemented in C and are very fast.
1122 This function doesn't have much to do with databases, except that it
1124 can sometimes be handy to store such values in a database. It also
1125 doesn't have much to do with perl hashes, like %foo.
1126 "sql_type_cast"
1128 $sts = DBI::sql_type_cast($sv, $sql_type, $flags);
1130 sql_type_cast attempts to cast $sv to the SQL type (see DBI Constants)
1132 specified in $sql_type. At present only the SQL types "SQL_INTEGER",
1133 "SQL_DOUBLE" and "SQL_NUMERIC" are supported.
1134 For "SQL_INTEGER" the effect is similar to using the value in an
1136 expression that requires an integer. It gives the perl scalar an
1137 'integer aspect'. (Technically the value gains an IV, or possibly a UV
1138 or NV if the value is too large for an IV.)
1139 For "SQL_DOUBLE" the effect is similar to using the value in an
1141 expression that requires a general numeric value. It gives the perl
1142 scalar a 'numeric aspect'. (Technically the value gains an NV.)
1143 "SQL_NUMERIC" is similar to "SQL_INTEGER" or "SQL_DOUBLE" but more
1145 general and more cautious. It will look at the string first and if it
1146 looks like an integer (that will fit in an IV or UV) it will act like
1147 "SQL_INTEGER", if it looks like a floating point value it will act like
1148 "SQL_DOUBLE", if it looks like neither then it will do nothing - and
1149 thereby avoid the warnings that would be generated by "SQL_INTEGER" and
1150 "SQL_DOUBLE" when given non-numeric data.
1151 $flags may be:
1153 "DBIstcf_DISCARD_STRING"
1155 If this flag is specified then when the driver successfully casts
1156 the bound perl scalar to a non-string type then the string portion
1157 of the scalar will be discarded.
1158 "DBIstcf_STRICT"
1160 If $sv cannot be cast to the requested $sql_type then by default it
1161 is left untouched and no error is generated. If you specify
1162 "DBIstcf_STRICT" and the cast fails, this will generate an error.
1163 The returned $sts value is:
1165 -2 sql_type is not handled
1167 -1 sv is undef so unchanged
1168 0 sv could not be cast cleanly and DBIstcf_STRICT was used
1169 1 sv could not be cast and DBIstcf_STRICT was not used
1170 2 sv was cast successfully
1171 This method is exported by the :utils tag and was introduced in DBI
1173 1.611.
1174 DBI Dynamic Attributes
1176 Dynamic attributes are always associated with the last handle used
1177 (that handle is represented by $h in the descriptions below).
1178 Where an attribute is equivalent to a method call, then refer to the
1180 method call for all related documentation.
1181 Warning: these attributes are provided as a convenience but they do
1183 have limitations. Specifically, they have a short lifespan: because
1184 they are associated with the last handle used, they should only be used
1185 immediately after calling the method that "sets" them. If in any
1186 doubt, use the corresponding method call.
1187 $DBI::err
1189 Equivalent to "$h->err".
1191 $DBI::errstr
1193 Equivalent to "$h->errstr".
1195 $DBI::state
1197 Equivalent to "$h->state".
1199 $DBI::rows
1201 Equivalent to "$h->rows". Please refer to the documentation for the
1203 "rows" method.
1204 $DBI::lasth
1206 Returns the DBI object handle used for the most recent DBI method call.
1208 If the last DBI method call was a DESTROY then $DBI::lasth will return
1209 the handle of the parent of the destroyed handle, if there is one.
1210
1212 The following methods can be used by all types of DBI handles.
1213 "err"
1215 $rv = $h->err;
1217 Returns the native database engine error code from the last driver
1219 method called. The code is typically an integer but you should not
1220 assume that.
1221 The DBI resets $h->err to undef before almost all DBI method calls, so
1223 the value only has a short lifespan. Also, for most drivers, the
1224 statement handles share the same error variable as the parent database
1225 handle, so calling a method on one handle may reset the error on the
1226 related handles.
1227 (Methods which don't reset err before being called include err() and
1229 errstr(), obviously, state(), rows(), func(), trace(), trace_msg(),
1230 ping(), and the tied hash attribute FETCH() and STORE() methods.)
1231 If you need to test for specific error conditions and have your program
1233 be portable to different database engines, then you'll need to
1234 determine what the corresponding error codes are for all those engines
1235 and test for all of them.
1236 The DBI uses the value of $DBI::stderr as the "err" value for internal
1238 errors. Drivers should also do likewise. The default value for
1239 $DBI::stderr is 2000000000.
1240 A driver may return 0 from err() to indicate a warning condition after
1242 a method call. Similarly, a driver may return an empty string to
1243 indicate a 'success with information' condition. In both these cases
1244 the value is false but not undef. The errstr() and state() methods may
1245 be used to retrieve extra information in these cases.
1246 See "set_err" for more information.
1248 "errstr"
1250 $str = $h->errstr;
1252 Returns the native database engine error message from the last DBI
1254 method called. This has the same lifespan issues as the "err" method
1255 described above.
1256 The returned string may contain multiple messages separated by newline
1258 characters.
1259 The errstr() method should not be used to test for errors, use err()
1261 for that, because drivers may return 'success with information' or
1262 warning messages via errstr() for methods that have not 'failed'.
1263 See "set_err" for more information.
1265 "state"
1267 $str = $h->state;
1269 Returns a state code in the standard SQLSTATE five character format.
1271 Note that the specific success code 00000 is translated to any empty
1272 string (false). If the driver does not support SQLSTATE (and most
1273 don't), then state() will return "S1000" (General Error) for all
1274 errors.
1275 The driver is free to return any value via "state", e.g., warning
1277 codes, even if it has not declared an error by returning a true value
1278 via the "err" method described above.
1279 The state() method should not be used to test for errors, use err() for
1281 that, because drivers may return a 'success with information' or
1282 warning state code via state() for methods that have not 'failed'.
1283 "set_err"
1285 $rv = $h->set_err($err, $errstr);
1287 $rv = $h->set_err($err, $errstr, $state);
1288 $rv = $h->set_err($err, $errstr, $state, $method);
1289 $rv = $h->set_err($err, $errstr, $state, $method, $rv);
1290 Set the "err", "errstr", and "state" values for the handle. This
1292 method is typically only used by DBI drivers and DBI subclasses.
1293 If the "HandleSetErr" attribute holds a reference to a subroutine it is
1295 called first. The subroutine can alter the $err, $errstr, $state, and
1296 $method values. See "HandleSetErr" for full details. If the subroutine
1297 returns a true value then the handle "err", "errstr", and "state"
1298 values are not altered and set_err() returns an empty list (it normally
1299 returns $rv which defaults to undef, see below).
1300 Setting "err" to a true value indicates an error and will trigger the
1302 normal DBI error handling mechanisms, such as "RaiseError" and
1303 "HandleError", if they are enabled, when execution returns from the DBI
1304 back to the application.
1305 Setting "err" to "" indicates an 'information' state, and setting it to
1307 "0" indicates a 'warning' state. Setting "err" to "undef" also sets
1308 "errstr" to undef, and "state" to "", irrespective of the values of the
1309 $errstr and $state parameters.
1310 The $method parameter provides an alternate method name for the
1312 "RaiseError"/"PrintError"/"PrintWarn" error string instead of the
1313 fairly unhelpful '"set_err"'.
1314 The "set_err" method normally returns undef. The $rv parameter
1316 provides an alternate return value.
1317 Some special rules apply if the "err" or "errstr" values for the handle
1319 are already set...
1320 If "errstr" is true then: "" [err was %s now %s]"" is appended if $err
1322 is true and "err" is already true and the new err value differs from
1323 the original one. Similarly "" [state was %s now %s]"" is appended if
1324 $state is true and "state" is already true and the new state value
1325 differs from the original one. Finally ""\n"" and the new $errstr are
1326 appended if $errstr differs from the existing errstr value. Obviously
1327 the %s's above are replaced by the corresponding values.
1328 The handle "err" value is set to $err if: $err is true; or handle "err"
1330 value is undef; or $err is defined and the length is greater than the
1331 handle "err" length. The effect is that an 'information' state only
1332 overrides undef; a 'warning' overrides undef or 'information', and an
1333 'error' state overrides anything.
1334 The handle "state" value is set to $state if $state is true and the
1336 handle "err" value was set (by the rules above).
1337 Support for warning and information states was added in DBI 1.41.
1339 "trace"
1341 $h->trace($trace_settings);
1343 $h->trace($trace_settings, $trace_filename);
1344 $trace_settings = $h->trace;
1345 The trace() method is used to alter the trace settings for a handle
1347 (and any future children of that handle). It can also be used to
1348 change where the trace output is sent.
1349 There's a similar method, "DBI->trace", which sets the global default
1351 trace settings.
1352 See the "TRACING" section for full details about the DBI's powerful
1354 tracing facilities.
1355 "trace_msg"
1357 $h->trace_msg($message_text);
1359 $h->trace_msg($message_text, $min_level);
1360 Writes $message_text to the trace file if the trace level is greater
1362 than or equal to $min_level (which defaults to 1). Can also be called
1363 as "DBI->trace_msg($msg)".
1364 See "TRACING" for more details.
1366 "func"
1368 $h->func(@func_arguments, $func_name) or die ...;
1370 The "func" method can be used to call private non-standard and non-
1372 portable methods implemented by the driver. Note that the function name
1373 is given as the last argument.
1374 It's also important to note that the func() method does not clear a
1376 previous error ($DBI::err etc.) and it does not trigger automatic error
1377 detection (RaiseError etc.) so you must check the return status and/or
1378 $h->err to detect errors.
1379 (This method is not directly related to calling stored procedures.
1381 Calling stored procedures is currently not defined by the DBI. Some
1382 drivers, such as DBD::Oracle, support it in non-portable ways. See
1383 driver documentation for more details.)
1384 See also install_method() in DBI::DBD for how you can avoid needing to
1386 use func() and gain direct access to driver-private methods.
1387 "can"
1389 $is_implemented = $h->can($method_name);
1391 Returns true if $method_name is implemented by the driver or a default
1393 method is provided by the DBI's driver base class. It returns false
1394 where a driver hasn't implemented a method and the default method is
1395 provided by the DBI's driver base class is just an empty stub.
1396 "parse_trace_flags"
1398 $trace_settings_integer = $h->parse_trace_flags($trace_settings);
1400 Parses a string containing trace settings and returns the corresponding
1402 integer value used internally by the DBI and drivers.
1403 The $trace_settings argument is a string containing a trace level
1405 between 0 and 15 and/or trace flag names separated by vertical bar
1406 (""|"") or comma ("","") characters. For example: "SQL|3|foo".
1407 It uses the parse_trace_flag() method, described below, to process the
1409 individual trace flag names.
1410 The parse_trace_flags() method was added in DBI 1.42.
1412 "parse_trace_flag"
1414 $bit_flag = $h->parse_trace_flag($trace_flag_name);
1416 Returns the bit flag corresponding to the trace flag name in
1418 $trace_flag_name. Drivers are expected to override this method and
1419 check if $trace_flag_name is a driver specific trace flags and, if not,
1420 then call the DBI's default parse_trace_flag().
1421 The parse_trace_flag() method was added in DBI 1.42.
1423 "private_attribute_info"
1425 $hash_ref = $h->private_attribute_info();
1427 Returns a reference to a hash whose keys are the names of driver-
1429 private handle attributes available for the kind of handle (driver,
1430 database, statement) that the method was called on.
1431 For example, the return value when called with a DBD::Sybase $dbh could
1433 look like this:
1434 {
1436 syb_dynamic_supported => undef,
1437 syb_oc_version => undef,
1438 syb_server_version => undef,
1439 syb_server_version_string => undef,
1440 }
1441 and when called with a DBD::Sybase $sth they could look like this:
1443 {
1445 syb_types => undef,
1446 syb_proc_status => undef,
1447 syb_result_type => undef,
1448 }
1449 The values should be undef. Meanings may be assigned to particular
1451 values in future.
1452 "swap_inner_handle"
1454 $rc = $h1->swap_inner_handle( $h2 );
1456 $rc = $h1->swap_inner_handle( $h2, $allow_reparent );
1457 Brain transplants for handles. You don't need to know about this unless
1459 you want to become a handle surgeon.
1460 A DBI handle is a reference to a tied hash. A tied hash has an inner
1462 hash that actually holds the contents. The swap_inner_handle() method
1463 swaps the inner hashes between two handles. The $h1 and $h2 handles
1464 still point to the same tied hashes, but what those hashes are tied to
1465 has been swapped. In effect $h1 becomes $h2 and vice-versa. This is
1466 powerful stuff, expect problems. Use with care.
1467 As a small safety measure, the two handles, $h1 and $h2, have to share
1469 the same parent unless $allow_reparent is true.
1470 The swap_inner_handle() method was added in DBI 1.44.
1472 Here's a quick kind of 'diagram' as a worked example to help think
1474 about what's happening:
1475 Original state:
1477 dbh1o -> dbh1i
1478 sthAo -> sthAi(dbh1i)
1479 dbh2o -> dbh2i
1480 swap_inner_handle dbh1o with dbh2o:
1482 dbh2o -> dbh1i
1483 sthAo -> sthAi(dbh1i)
1484 dbh1o -> dbh2i
1485 create new sth from dbh1o:
1487 dbh2o -> dbh1i
1488 sthAo -> sthAi(dbh1i)
1489 dbh1o -> dbh2i
1490 sthBo -> sthBi(dbh2i)
1491 swap_inner_handle sthAo with sthBo:
1493 dbh2o -> dbh1i
1494 sthBo -> sthAi(dbh1i)
1495 dbh1o -> dbh2i
1496 sthAo -> sthBi(dbh2i)
1497 "visit_child_handles"
1499 $h->visit_child_handles( $coderef );
1501 $h->visit_child_handles( $coderef, $info );
1502 Where $coderef is a reference to a subroutine and $info is an arbitrary
1504 value which, if undefined, defaults to a reference to an empty hash.
1505 Returns $info.
1506 For each child handle of $h, if any, $coderef is invoked as:
1508 $coderef->($child_handle, $info);
1510 If the execution of $coderef returns a true value then
1512 "visit_child_handles" is called on that child handle and passed the
1513 returned value as $info.
1514 For example:
1516 # count database connections with names (DSN) matching a pattern
1518 my $connections = 0;
1519 $dbh->{Driver}->visit_child_handles(sub {
1520 my ($h, $info) = @_;
1521 ++$connections if $h->{Name} =~ /foo/;
1522 return 0; # don't visit kids
1523 })
1524 See also "visit_handles".
1526
1528 These attributes are common to all types of DBI handles.
1529 Some attributes are inherited by child handles. That is, the value of
1531 an inherited attribute in a newly created statement handle is the same
1532 as the value in the parent database handle. Changes to attributes in
1533 the new statement handle do not affect the parent database handle and
1534 changes to the database handle do not affect existing statement
1535 handles, only future ones.
1536 Attempting to set or get the value of an unknown attribute generates a
1538 warning, except for private driver specific attributes (which all have
1539 names starting with a lowercase letter).
1540 Example:
1542 $h->{AttributeName} = ...; # set/write
1544 ... = $h->{AttributeName}; # get/read
1545 "Warn"
1547 Type: boolean, inherited
1549 The "Warn" attribute enables useful warnings for certain bad practices.
1551 It is enabled by default and should only be disabled in rare
1552 circumstances. Since warnings are generated using the Perl "warn"
1553 function, they can be intercepted using the Perl $SIG{__WARN__} hook.
1554 The "Warn" attribute is not related to the "PrintWarn" attribute.
1556 "Active"
1558 Type: boolean, read-only
1560 The "Active" attribute is true if the handle object is "active". This
1562 is rarely used in applications. The exact meaning of active is somewhat
1563 vague at the moment. For a database handle it typically means that the
1564 handle is connected to a database ("$dbh->disconnect" sets "Active"
1565 off). For a statement handle it typically means that the handle is a
1566 "SELECT" that may have more data to fetch. (Fetching all the data or
1567 calling "$sth->finish" sets "Active" off.)
1568 "Executed"
1570 Type: boolean
1572 The "Executed" attribute is true if the handle object has been
1574 "executed". Currently only the $dbh do() method and the $sth
1575 execute(), execute_array(), and execute_for_fetch() methods set the
1576 "Executed" attribute.
1577 When it's set on a handle it is also set on the parent handle at the
1579 same time. So calling execute() on a $sth also sets the "Executed"
1580 attribute on the parent $dbh.
1581 The "Executed" attribute for a database handle is cleared by the
1583 commit() and rollback() methods (even if they fail). The "Executed"
1584 attribute of a statement handle is not cleared by the DBI under any
1585 circumstances and so acts as a permanent record of whether the
1586 statement handle was ever used.
1587 The "Executed" attribute was added in DBI 1.41.
1589 "Kids"
1591 Type: integer, read-only
1593 For a driver handle, "Kids" is the number of currently existing
1595 database handles that were created from that driver handle. For a
1596 database handle, "Kids" is the number of currently existing statement
1597 handles that were created from that database handle. For a statement
1598 handle, the value is zero.
1599 "ActiveKids"
1601 Type: integer, read-only
1603 Like "Kids", but only counting those that are "Active" (as above).
1605 "CachedKids"
1607 Type: hash ref
1609 For a database handle, "CachedKids" returns a reference to the cache
1611 (hash) of statement handles created by the "prepare_cached" method.
1612 For a driver handle, returns a reference to the cache (hash) of
1613 database handles created by the "connect_cached" method.
1614 "Type"
1616 Type: scalar, read-only
1618 The "Type" attribute identifies the type of a DBI handle. Returns "dr"
1620 for driver handles, "db" for database handles and "st" for statement
1621 handles.
1622 "ChildHandles"
1624 Type: array ref
1626 The ChildHandles attribute contains a reference to an array of all the
1628 handles created by this handle which are still accessible. The
1629 contents of the array are weak-refs and will become undef when the
1630 handle goes out of scope. (They're cleared out occasionally.)
1631 "ChildHandles" returns undef if your perl version does not support weak
1633 references (check the Scalar::Util module). The referenced array
1634 returned should be treated as read-only.
1635 For example, to enumerate all driver handles, database handles and
1637 statement handles:
1638 sub show_child_handles {
1640 my ($h, $level) = @_;
1641 printf "%sh %s %s\n", $h->{Type}, "\t" x $level, $h;
1642 show_child_handles($_, $level + 1)
1643 for (grep { defined } @{$h->{ChildHandles}});
1644 }
1645 my %drivers = DBI->installed_drivers();
1647 show_child_handles($_, 0) for (values %drivers);
1648 "CompatMode"
1650 Type: boolean, inherited
1652 The "CompatMode" attribute is used by emulation layers (such as
1654 Oraperl) to enable compatible behaviour in the underlying driver (e.g.,
1655 DBD::Oracle) for this handle. Not normally set by application code.
1656 It also has the effect of disabling the 'quick FETCH' of attribute
1658 values from the handles attribute cache. So all attribute values are
1659 handled by the drivers own FETCH method. This makes them slightly
1660 slower but is useful for special-purpose drivers like DBD::Multiplex.
1661 "InactiveDestroy"
1663 Type: boolean
1665 The default value, false, means a handle will be fully destroyed as
1667 normal when the last reference to it is removed, just as you'd expect.
1668 If set true then the handle will be treated by the DESTROY as if it was
1670 no longer Active, and so the database engine related effects of
1671 DESTROYing a handle will be skipped. Think of the name as meaning
1672 'treat the handle as not-Active in the DESTROY method'.
1673 For a database handle, this attribute does not disable an explicit call
1675 to the disconnect method, only the implicit call from DESTROY that
1676 happens if the handle is still marked as "Active".
1677 This attribute is specifically designed for use in Unix applications
1679 that "fork" child processes. For some drivers, when the child process
1680 exits the destruction of inherited handles cause the corresponding
1681 handles in the parent process to cease working.
1682 Either the parent or the child process, but not both, should set
1684 "InactiveDestroy" true on all their shared handles. Alternatively, and
1685 preferably, the "AutoInactiveDestroy" can be set in the parent on
1686 connect.
1687 To help tracing applications using fork the process id is shown in the
1689 trace log whenever a DBI or handle trace() method is called. The
1690 process id also shown for every method call if the DBI trace level (not
1691 handle trace level) is set high enough to show the trace from the DBI's
1692 method dispatcher, e.g. >= 9.
1693 "AutoInactiveDestroy"
1695 Type: boolean, inherited
1697 The "InactiveDestroy" attribute, described above, needs to be
1699 explicitly set in the child process after a fork(), on every active
1700 database and statement handle. This is a problem if the code that
1701 performs the fork() is not under your control, perhaps in a third-party
1702 module. Use "AutoInactiveDestroy" to get around this situation.
1703 If set true, the DESTROY method will check the process id of the handle
1705 and, if different from the current process id, it will set the
1706 InactiveDestroy attribute. It is strongly recommended that
1707 "AutoInactiveDestroy" is enabled on all new code (it's only not enabled
1708 by default to avoid backwards compatibility problems).
1709 This is the example it's designed to deal with:
1711 my $dbh = DBI->connect(...);
1713 some_code_that_forks(); # Perhaps without your knowledge
1714 # Child process dies, destroying the inherited dbh
1715 $dbh->do(...); # Breaks because parent $dbh is now broken
1716 The "AutoInactiveDestroy" attribute was added in DBI 1.614.
1718 "PrintWarn"
1720 Type: boolean, inherited
1722 The "PrintWarn" attribute controls the printing of warnings recorded by
1724 the driver. When set to a true value (the default) the DBI will check
1725 method calls to see if a warning condition has been set. If so, the DBI
1726 will effectively do a "warn("$class $method warning: $DBI::errstr")"
1727 where $class is the driver class and $method is the name of the method
1728 which failed. E.g.,
1729 DBD::Oracle::db execute warning: ... warning text here ...
1731 If desired, the warnings can be caught and processed using a
1733 $SIG{__WARN__} handler or modules like CGI::Carp and CGI::ErrorWrap.
1734 See also "set_err" for how warnings are recorded and "HandleSetErr" for
1736 how to influence it.
1737 Fetching the full details of warnings can require an extra round-trip
1739 to the database server for some drivers. In which case the driver may
1740 opt to only fetch the full details of warnings if the "PrintWarn"
1741 attribute is true. If "PrintWarn" is false then these drivers should
1742 still indicate the fact that there were warnings by setting the warning
1743 string to, for example: "3 warnings".
1744 "PrintError"
1746 Type: boolean, inherited
1748 The "PrintError" attribute can be used to force errors to generate
1750 warnings (using "warn") in addition to returning error codes in the
1751 normal way. When set "on", any method which results in an error
1752 occurring will cause the DBI to effectively do a "warn("$class $method
1753 failed: $DBI::errstr")" where $class is the driver class and $method is
1754 the name of the method which failed. E.g.,
1755 DBD::Oracle::db prepare failed: ... error text here ...
1757 By default, "DBI->connect" sets "PrintError" "on".
1759 If desired, the warnings can be caught and processed using a
1761 $SIG{__WARN__} handler or modules like CGI::Carp and CGI::ErrorWrap.
1762 "RaiseError"
1764 Type: boolean, inherited
1766 The "RaiseError" attribute can be used to force errors to raise
1768 exceptions rather than simply return error codes in the normal way. It
1769 is "off" by default. When set "on", any method which results in an
1770 error will cause the DBI to effectively do a "die("$class $method
1771 failed: $DBI::errstr")", where $class is the driver class and $method
1772 is the name of the method that failed. E.g.,
1773 DBD::Oracle::db prepare failed: ... error text here ...
1775 If you turn "RaiseError" on then you'd normally turn "PrintError" off.
1777 If "PrintError" is also on, then the "PrintError" is done first
1778 (naturally).
1779 Typically "RaiseError" is used in conjunction with "eval", or a module
1781 like Try::Tiny or TryCatch, to catch the exception that's been thrown
1782 and handle it. For example:
1783 use Try::Tiny;
1785 try {
1787 ...
1788 $sth->execute();
1789 ...
1790 } catch {
1791 # $sth->err and $DBI::err will be true if error was from DBI
1792 warn $_; # print the error (which Try::Tiny puts into $_)
1793 ... # do whatever you need to deal with the error
1794 };
1795 In the catch block the $DBI::lasth variable can be useful for diagnosis
1797 and reporting if you can't be sure which handle triggered the error.
1798 For example, $DBI::lasth->{Type} and $DBI::lasth->{Statement}.
1799 See also "Transactions".
1801 If you want to temporarily turn "RaiseError" off (inside a library
1803 function that is likely to fail, for example), the recommended way is
1804 like this:
1805 {
1807 local $h->{RaiseError}; # localize and turn off for this block
1808 ...
1809 }
1810 The original value will automatically and reliably be restored by Perl,
1812 regardless of how the block is exited. The same logic applies to other
1813 attributes, including "PrintError".
1814 "HandleError"
1816 Type: code ref, inherited
1818 The "HandleError" attribute can be used to provide your own alternative
1820 behaviour in case of errors. If set to a reference to a subroutine then
1821 that subroutine is called when an error is detected (at the same point
1822 that "RaiseError" and "PrintError" are handled).
1823 The subroutine is called with three parameters: the error message
1825 string that "RaiseError" and "PrintError" would use, the DBI handle
1826 being used, and the first value being returned by the method that
1827 failed (typically undef).
1828 If the subroutine returns a false value then the "RaiseError" and/or
1830 "PrintError" attributes are checked and acted upon as normal.
1831 For example, to "die" with a full stack trace for any error:
1833 use Carp;
1835 $h->{HandleError} = sub { confess(shift) };
1836 Or to turn errors into exceptions:
1838 use Exception; # or your own favourite exception module
1840 $h->{HandleError} = sub { Exception->new('DBI')->raise($_[0]) };
1841 It is possible to 'stack' multiple HandleError handlers by using
1843 closures:
1844 sub your_subroutine {
1846 my $previous_handler = $h->{HandleError};
1847 $h->{HandleError} = sub {
1848 return 1 if $previous_handler and &$previous_handler(@_);
1849 ... your code here ...
1850 };
1851 }
1852 Using a "my" inside a subroutine to store the previous "HandleError"
1854 value is important. See perlsub and perlref for more information about
1855 closures.
1856 It is possible for "HandleError" to alter the error message that will
1858 be used by "RaiseError" and "PrintError" if it returns false. It can
1859 do that by altering the value of $_[0]. This example appends a stack
1860 trace to all errors and, unlike the previous example using
1861 Carp::confess, this will work "PrintError" as well as "RaiseError":
1862 $h->{HandleError} = sub { $_[0]=Carp::longmess($_[0]); 0; };
1864 It is also possible for "HandleError" to hide an error, to a limited
1866 degree, by using "set_err" to reset $DBI::err and $DBI::errstr, and
1867 altering the return value of the failed method. For example:
1868 $h->{HandleError} = sub {
1870 return 0 unless $_[0] =~ /^\S+ fetchrow_arrayref failed:/;
1871 return 0 unless $_[1]->err == 1234; # the error to 'hide'
1872 $h->set_err(undef,undef); # turn off the error
1873 $_[2] = [ ... ]; # supply alternative return value
1874 return 1;
1875 };
1876 This only works for methods which return a single value and is hard to
1878 make reliable (avoiding infinite loops, for example) and so isn't
1879 recommended for general use! If you find a good use for it then please
1880 let me know.
1881 "HandleSetErr"
1883 Type: code ref, inherited
1885 The "HandleSetErr" attribute can be used to intercept the setting of
1887 handle "err", "errstr", and "state" values. If set to a reference to a
1888 subroutine then that subroutine is called whenever set_err() is called,
1889 typically by the driver or a subclass.
1890 The subroutine is called with five arguments, the first five that were
1892 passed to set_err(): the handle, the "err", "errstr", and "state"
1893 values being set, and the method name. These can be altered by changing
1894 the values in the @_ array. The return value affects set_err()
1895 behaviour, see "set_err" for details.
1896 It is possible to 'stack' multiple HandleSetErr handlers by using
1898 closures. See "HandleError" for an example.
1899 The "HandleSetErr" and "HandleError" subroutines differ in subtle but
1901 significant ways. HandleError is only invoked at the point where the
1902 DBI is about to return to the application with "err" set true. It's
1903 not invoked by the failure of a method that's been called by another
1904 DBI method. HandleSetErr, on the other hand, is called whenever
1905 set_err() is called with a defined "err" value, even if false. So it's
1906 not just for errors, despite the name, but also warn and info states.
1907 The set_err() method, and thus HandleSetErr, may be called multiple
1908 times within a method and is usually invoked from deep within driver
1909 code.
1910 In theory a driver can use the return value from HandleSetErr via
1912 set_err() to decide whether to continue or not. If set_err() returns an
1913 empty list, indicating that the HandleSetErr code has 'handled' the
1914 'error', the driver could then continue instead of failing (if that's a
1915 reasonable thing to do). This isn't excepted to be common and any such
1916 cases should be clearly marked in the driver documentation and
1917 discussed on the dbi-dev mailing list.
1918 The "HandleSetErr" attribute was added in DBI 1.41.
1920 "ErrCount"
1922 Type: unsigned integer
1924 The "ErrCount" attribute is incremented whenever the set_err() method
1926 records an error. It isn't incremented by warnings or information
1927 states. It is not reset by the DBI at any time.
1928 The "ErrCount" attribute was added in DBI 1.41. Older drivers may not
1930 have been updated to use set_err() to record errors and so this
1931 attribute may not be incremented when using them.
1932 "ShowErrorStatement"
1934 Type: boolean, inherited
1936 The "ShowErrorStatement" attribute can be used to cause the relevant
1938 Statement text to be appended to the error messages generated by the
1939 "RaiseError", "PrintError", and "PrintWarn" attributes. Only applies
1940 to errors on statement handles plus the prepare(), do(), and the
1941 various "select*()" database handle methods. (The exact format of the
1942 appended text is subject to change.)
1943 If "$h->{ParamValues}" returns a hash reference of parameter
1945 (placeholder) values then those are formatted and appended to the end
1946 of the Statement text in the error message.
1947 "TraceLevel"
1949 Type: integer, inherited
1951 The "TraceLevel" attribute can be used as an alternative to the "trace"
1953 method to set the DBI trace level and trace flags for a specific
1954 handle. See "TRACING" for more details.
1955 The "TraceLevel" attribute is especially useful combined with "local"
1957 to alter the trace settings for just a single block of code.
1958 "FetchHashKeyName"
1960 Type: string, inherited
1962 The "FetchHashKeyName" attribute is used to specify whether the
1964 fetchrow_hashref() method should perform case conversion on the field
1965 names used for the hash keys. For historical reasons it defaults to
1966 '"NAME"' but it is recommended to set it to '"NAME_lc"' (convert to
1967 lower case) or '"NAME_uc"' (convert to upper case) according to your
1968 preference. It can only be set for driver and database handles. For
1969 statement handles the value is frozen when prepare() is called.
1970 "ChopBlanks"
1972 Type: boolean, inherited
1974 The "ChopBlanks" attribute can be used to control the trimming of
1976 trailing space characters from fixed width character (CHAR) fields. No
1977 other field types are affected, even where field values have trailing
1978 spaces.
1979 The default is false (although it is possible that the default may
1981 change). Applications that need specific behaviour should set the
1982 attribute as needed.
1983 Drivers are not required to support this attribute, but any driver
1985 which does not support it must arrange to return "undef" as the
1986 attribute value.
1987 "LongReadLen"
1989 Type: unsigned integer, inherited
1991 The "LongReadLen" attribute may be used to control the maximum length
1993 of 'long' type fields (LONG, BLOB, CLOB, MEMO, etc.) which the driver
1994 will read from the database automatically when it fetches each row of
1995 data.
1996 The "LongReadLen" attribute only relates to fetching and reading long
1998 values; it is not involved in inserting or updating them.
1999 A value of 0 means not to automatically fetch any long data. Drivers
2001 may return undef or an empty string for long fields when "LongReadLen"
2002 is 0.
2003 The default is typically 0 (zero) or 80 bytes but may vary between
2005 drivers. Applications fetching long fields should set this value to
2006 slightly larger than the longest long field value to be fetched.
2007 Some databases return some long types encoded as pairs of hex digits.
2009 For these types, "LongReadLen" relates to the underlying data length
2010 and not the doubled-up length of the encoded string.
2011 Changing the value of "LongReadLen" for a statement handle after it has
2013 been "prepare"'d will typically have no effect, so it's common to set
2014 "LongReadLen" on the $dbh before calling "prepare".
2015 For most drivers the value used here has a direct effect on the memory
2017 used by the statement handle while it's active, so don't be too
2018 generous. If you can't be sure what value to use you could execute an
2019 extra select statement to determine the longest value. For example:
2020 $dbh->{LongReadLen} = $dbh->selectrow_array(qq{
2022 SELECT MAX(OCTET_LENGTH(long_column_name))
2023 FROM table WHERE ...
2024 });
2025 $sth = $dbh->prepare(qq{
2026 SELECT long_column_name, ... FROM table WHERE ...
2027 });
2028 You may need to take extra care if the table can be modified between
2030 the first select and the second being executed. You may also need to
2031 use a different function if OCTET_LENGTH() does not work for long types
2032 in your database. For example, for Sybase use DATALENGTH() and for
2033 Oracle use LENGTHB().
2034 See also "LongTruncOk" for information on truncation of long types.
2036 "LongTruncOk"
2038 Type: boolean, inherited
2040 The "LongTruncOk" attribute may be used to control the effect of
2042 fetching a long field value which has been truncated (typically because
2043 it's longer than the value of the "LongReadLen" attribute).
2044 By default, "LongTruncOk" is false and so fetching a long value that
2046 needs to be truncated will cause the fetch to fail. (Applications
2047 should always be sure to check for errors after a fetch loop in case an
2048 error, such as a divide by zero or long field truncation, caused the
2049 fetch to terminate prematurely.)
2050 If a fetch fails due to a long field truncation when "LongTruncOk" is
2052 false, many drivers will allow you to continue fetching further rows.
2053 See also "LongReadLen".
2055 "TaintIn"
2057 Type: boolean, inherited
2059 If the "TaintIn" attribute is set to a true value and Perl is running
2061 in taint mode (e.g., started with the "-T" option), then all the
2062 arguments to most DBI method calls are checked for being tainted. This
2063 may change.
2064 The attribute defaults to off, even if Perl is in taint mode. See
2066 perlsec for more about taint mode. If Perl is not running in taint
2067 mode, this attribute has no effect.
2068 When fetching data that you trust you can turn off the TaintIn
2070 attribute, for that statement handle, for the duration of the fetch
2071 loop.
2072 The "TaintIn" attribute was added in DBI 1.31.
2074 "TaintOut"
2076 Type: boolean, inherited
2078 If the "TaintOut" attribute is set to a true value and Perl is running
2080 in taint mode (e.g., started with the "-T" option), then most data
2081 fetched from the database is considered tainted. This may change.
2082 The attribute defaults to off, even if Perl is in taint mode. See
2084 perlsec for more about taint mode. If Perl is not running in taint
2085 mode, this attribute has no effect.
2086 When fetching data that you trust you can turn off the TaintOut
2088 attribute, for that statement handle, for the duration of the fetch
2089 loop.
2090 Currently only fetched data is tainted. It is possible that the results
2092 of other DBI method calls, and the value of fetched attributes, may
2093 also be tainted in future versions. That change may well break your
2094 applications unless you take great care now. If you use DBI Taint mode,
2095 please report your experience and any suggestions for changes.
2096 The "TaintOut" attribute was added in DBI 1.31.
2098 "Taint"
2100 Type: boolean, inherited
2102 The "Taint" attribute is a shortcut for "TaintIn" and "TaintOut" (it is
2104 also present for backwards compatibility).
2105 Setting this attribute sets both "TaintIn" and "TaintOut", and
2107 retrieving it returns a true value if and only if "TaintIn" and
2108 "TaintOut" are both set to true values.
2109 "Profile"
2111 Type: inherited
2113 The "Profile" attribute enables the collection and reporting of method
2115 call timing statistics. See the DBI::Profile module documentation for
2116 much more detail.
2117 The "Profile" attribute was added in DBI 1.24.
2119 "ReadOnly"
2121 Type: boolean, inherited
2123 An application can set the "ReadOnly" attribute of a handle to a true
2125 value to indicate that it will not be attempting to make any changes
2126 using that handle or any children of it.
2127 Note that the exact definition of 'read only' is rather fuzzy. For
2129 more details see the documentation for the driver you're using.
2130 If the driver can make the handle truly read-only then it should
2132 (unless doing so would have unpleasant side effect, like changing the
2133 consistency level from per-statement to per-session). Otherwise the
2134 attribute is simply advisory.
2135 A driver can set the "ReadOnly" attribute itself to indicate that the
2137 data it is connected to cannot be changed for some reason.
2138 If the driver cannot ensure the "ReadOnly" attribute is adhered to it
2140 will record a warning. In this case reading the "ReadOnly" attribute
2141 back after it is set true will return true even if the underlying
2142 driver cannot ensure this (so any application knows the application
2143 declared itself ReadOnly).
2144 Library modules and proxy drivers can use the attribute to influence
2146 their behavior. For example, the DBD::Gofer driver considers the
2147 "ReadOnly" attribute when making a decision about whether to retry an
2148 operation that failed.
2149 The attribute should be set to 1 or 0 (or undef). Other values are
2151 reserved.
2152 "Callbacks"
2154 Type: hash ref
2156 The DBI callback mechanism lets you intercept, and optionally replace,
2158 any method call on a DBI handle. At the extreme, it lets you become a
2159 puppet master, deceiving the application in any way you want.
2160 The "Callbacks" attribute is a hash reference where the keys are DBI
2162 method names and the values are code references. For each key naming a
2163 method, the DBI will execute the associated code reference before
2164 executing the method.
2165 The arguments to the code reference will be the same as to the method,
2167 including the invocant (a database handle or statement handle). For
2168 example, say that to callback to some code on a call to "prepare()":
2169 $dbh->{Callbacks} = {
2171 prepare => sub {
2172 my ($dbh, $query, $attrs) = @_;
2173 print "Preparing q{$query}\n"
2174 },
2175 };
2176 The callback would then be executed when you called the "prepare()"
2178 method:
2179 $dbh->prepare('SELECT 1');
2181 And the output of course would be:
2183 Preparing q{SELECT 1}
2185 Because callbacks are executed before the methods they're associated
2187 with, you can modify the arguments before they're passed on to the
2188 method call. For example, to make sure that all calls to "prepare()"
2189 are immediately prepared by DBD::Pg, add a callback that makes sure
2190 that the "pg_prepare_now" attribute is always set:
2191 my $dbh = DBI->connect($dsn, $username, $auth, {
2193 Callbacks => {
2194 prepare => sub {
2195 $_[2] ||= {};
2196 $_[2]->{pg_prepare_now} = 1;
2197 return; # must return nothing
2198 },
2199 }
2200 });
2201 Note that we are editing the contents of @_ directly. In this case
2203 we've created the attributes hash if it's not passed to the "prepare"
2204 call.
2205 You can also prevent the associated method from ever executing. While a
2207 callback executes, $_ holds the method name. (This allows multiple
2208 callbacks to share the same code reference and still know what method
2209 was called.) To prevent the method from executing, simply "undef $_".
2210 For example, if you wanted to disable calls to "ping()", you could do
2211 this:
2212 $dbh->{Callbacks} = {
2214 ping => sub {
2215 # tell dispatch to not call the method:
2216 undef $_;
2217 # return this value instead:
2218 return "42 bells";
2219 }
2220 };
2221 As with other attributes, Callbacks can be specified on a handle or via
2223 the attributes to "connect()". Callbacks can also be applied to a
2224 statement methods on a statement handle. For example:
2225 $sth->{Callbacks} = {
2227 execute => sub {
2228 print "Executing ", shift->{Statement}, "\n";
2229 }
2230 };
2231 The "Callbacks" attribute of a database handle isn't copied to any
2233 statement handles it creates. So setting callbacks for a statement
2234 handle requires you to set the "Callbacks" attribute on the statement
2235 handle yourself, as in the example above, or use the special
2236 "ChildCallbacks" key described below.
2237 Special Keys in Callbacks Attribute
2239 In addition to DBI handle method names, the "Callbacks" hash reference
2241 supports four additional keys.
2242 The first is the "ChildCallbacks" key. When a statement handle is
2244 created from a database handle the "ChildCallbacks" key of the database
2245 handle's "Callbacks" attribute, if any, becomes the new "Callbacks"
2246 attribute of the statement handle. This allows you to define callbacks
2247 for all statement handles created from a database handle. For example,
2248 if you wanted to count how many times "execute" was called in your
2249 application, you could write:
2250 my $exec_count = 0;
2252 my $dbh = DBI->connect( $dsn, $username, $auth, {
2253 Callbacks => {
2254 ChildCallbacks => {
2255 execute => sub { $exec_count++; return; }
2256 }
2257 }
2258 });
2259 END {
2261 print "The execute method was called $exec_count times\n";
2262 }
2263 The other three special keys are "connect_cached.new",
2265 "connect_cached.connected", and "connect_cached.reused". These keys
2266 define callbacks that are called when "connect_cached()" is called, but
2267 allow different behaviors depending on whether a new handle is created
2268 or a handle is returned. The callback is invoked with these arguments:
2269 "$dbh, $dsn, $user, $auth, $attr".
2270 For example, some applications uses "connect_cached()" to connect with
2272 "AutoCommit" enabled and then disable "AutoCommit" temporarily for
2273 transactions. If "connect_cached()" is called during a transaction,
2274 perhaps in a utility method, then it might select the same cached
2275 handle and then force "AutoCommit" on, forcing a commit of the
2276 transaction. See the "connect_cached" documentation for one way to deal
2277 with that. Here we'll describe an alternative approach using a
2278 callback.
2279 Because the "connect_cached.new" and "connect_cached.reused" callbacks
2281 are invoked before "connect_cached()" has applied the connect
2282 attributes, you can use them to edit the attributes that will be
2283 applied. To prevent a cached handle from having its transactions
2284 committed before it's returned, you can eliminate the "AutoCommit"
2285 attribute in a "connect_cached.reused" callback, like so:
2286 my $cb = {
2288 'connect_cached.reused' => sub { delete $_[4]->{AutoCommit} },
2289 };
2290 sub dbh {
2292 my $self = shift;
2293 DBI->connect_cached( $dsn, $username, $auth, {
2294 PrintError => 0,
2295 RaiseError => 1,
2296 AutoCommit => 1,
2297 Callbacks => $cb,
2298 });
2299 }
2300 The upshot is that new database handles are created with "AutoCommit"
2302 enabled, while cached database handles are left in whatever transaction
2303 state they happened to be in when retrieved from the cache.
2304 Note that we've also used a lexical for the callbacks hash reference.
2306 This is because "connect_cached()" returns a new database handle if any
2307 of the attributes passed to is have changed. If we used an inline hash
2308 reference, "connect_cached()" would return a new database handle every
2309 time. Which would rather defeat the purpose.
2310 A more common application for callbacks is setting connection state
2312 only when a new connection is made (by connect() or connect_cached()).
2313 Adding a callback to the connected method (when using "connect") or via
2314 "connect_cached.connected" (when useing connect_cached()>) makes this
2315 easy. The connected() method is a no-op by default (unless you
2316 subclass the DBI and change it). The DBI calls it to indicate that a
2317 new connection has been made and the connection attributes have all
2318 been set. You can give it a bit of added functionality by applying a
2319 callback to it. For example, to make sure that MySQL understands your
2320 application's ANSI-compliant SQL, set it up like so:
2321 my $dbh = DBI->connect($dsn, $username, $auth, {
2323 Callbacks => {
2324 connected => sub {
2325 shift->do(q{
2326 SET SESSION sql_mode='ansi,strict_trans_tables,no_auto_value_on_zero';
2327 });
2328 return;
2329 },
2330 }
2331 });
2332 If you're using "connect_cached()", use the "connect_cached.connected"
2334 callback, instead. This is because "connected()" is called for both new
2335 and reused database handles, but you want to execute a callback only
2336 the when a new database handle is returned. For example, to set the
2337 time zone on connection to a PostgreSQL database, try this:
2338 my $cb = {
2340 'connect_cached.connected' => sub {
2341 shift->do('SET timezone = UTC');
2342 }
2343 };
2344 sub dbh {
2346 my $self = shift;
2347 DBI->connect_cached( $dsn, $username, $auth, { Callbacks => $cb });
2348 }
2349 One significant limitation with callbacks is that there can only be one
2351 per method per handle. This means it's easy for one use of callbacks to
2352 interfere with, or typically simply overwrite, another use of
2353 callbacks. For this reason modules using callbacks should document the
2354 fact clearly so application authors can tell if use of callbacks by the
2355 module will clash with use of callbacks by the application.
2356 You might be able to work around this issue by taking a copy of the
2358 original callback and calling it within your own. For example:
2359 my $prev_cb = $h->{Callbacks}{method_name};
2361 $h->{Callbacks}{method_name} = sub {
2362 if ($prev_cb) {
2363 my @result = $prev_cb->(@_);
2364 return @result if not $_; # $prev_cb vetoed call
2365 }
2366 ... your callback logic here ...
2367 };
2368 "private_your_module_name_*"
2370 The DBI provides a way to store extra information in a DBI handle as
2372 "private" attributes. The DBI will allow you to store and retrieve any
2373 attribute which has a name starting with ""private_"".
2374 It is strongly recommended that you use just one private attribute
2376 (e.g., use a hash ref) and give it a long and unambiguous name that
2377 includes the module or application name that the attribute relates to
2378 (e.g., ""private_YourFullModuleName_thingy"").
2379 Because of the way the Perl tie mechanism works you cannot reliably use
2381 the "||=" operator directly to initialise the attribute, like this:
2382 my $foo = $dbh->{private_yourmodname_foo} ||= { ... }; # WRONG
2384 you should use a two step approach like this:
2386 my $foo = $dbh->{private_yourmodname_foo};
2388 $foo ||= $dbh->{private_yourmodname_foo} = { ... };
2389 This attribute is primarily of interest to people sub-classing DBI, or
2391 for applications to piggy-back extra information onto DBI handles.
2392
2394 This section covers the methods and attributes associated with database
2395 handles.
2396 Database Handle Methods
2398 The following methods are specified for DBI database handles:
2399 "clone"
2401 $new_dbh = $dbh->clone(\%attr);
2403 The "clone" method duplicates the $dbh connection by connecting with
2405 the same parameters ($dsn, $user, $password) as originally used.
2406 The attributes for the cloned connect are the same as those used for
2408 the original connect, with any other attributes in "\%attr" merged over
2409 them. Effectively the same as doing:
2410 %attributes_used = ( %original_attributes, %attr );
2412 If \%attr is not given then it defaults to a hash containing all the
2414 attributes in the attribute cache of $dbh excluding any non-code
2415 references, plus the main boolean attributes (RaiseError, PrintError,
2416 AutoCommit, etc.). This behaviour is unreliable and so use of clone
2417 without an argument is deprecated and may cause a warning in a future
2418 release.
2419 The clone method can be used even if the database handle is
2421 disconnected.
2422 The "clone" method was added in DBI 1.33.
2424 "data_sources"
2426 @ary = $dbh->data_sources();
2428 @ary = $dbh->data_sources(\%attr);
2429 Returns a list of data sources (databases) available via the $dbh
2431 driver's data_sources() method, plus any extra data sources that the
2432 driver can discover via the connected $dbh. Typically the extra data
2433 sources are other databases managed by the same server process that the
2434 $dbh is connected to.
2435 Data sources are returned in a form suitable for passing to the
2437 "connect" method (that is, they will include the ""dbi:$driver:""
2438 prefix).
2439 The data_sources() method, for a $dbh, was added in DBI 1.38.
2441 "do"
2443 $rows = $dbh->do($statement) or die $dbh->errstr;
2445 $rows = $dbh->do($statement, \%attr) or die $dbh->errstr;
2446 $rows = $dbh->do($statement, \%attr, @bind_values) or die ...
2447 Prepare and execute a single statement. Returns the number of rows
2449 affected or "undef" on error. A return value of "-1" means the number
2450 of rows is not known, not applicable, or not available.
2451 This method is typically most useful for non-"SELECT" statements that
2453 either cannot be prepared in advance (due to a limitation of the
2454 driver) or do not need to be executed repeatedly. It should not be used
2455 for "SELECT" statements because it does not return a statement handle
2456 (so you can't fetch any data).
2457 The default "do" method is logically similar to:
2459 sub do {
2461 my($dbh, $statement, $attr, @bind_values) = @_;
2462 my $sth = $dbh->prepare($statement, $attr) or return undef;
2463 $sth->execute(@bind_values) or return undef;
2464 my $rows = $sth->rows;
2465 ($rows == 0) ? "0E0" : $rows; # always return true if no error
2466 }
2467 For example:
2469 my $rows_deleted = $dbh->do(q{
2471 DELETE FROM table
2472 WHERE status = ?
2473 }, undef, 'DONE') or die $dbh->errstr;
2474 Using placeholders and @bind_values with the "do" method can be useful
2476 because it avoids the need to correctly quote any variables in the
2477 $statement. But if you'll be executing the statement many times then
2478 it's more efficient to "prepare" it once and call "execute" many times
2479 instead.
2480 The "q{...}" style quoting used in this example avoids clashing with
2482 quotes that may be used in the SQL statement. Use the double-quote-like
2483 "qq{...}" operator if you want to interpolate variables into the
2484 string. See "Quote and Quote-like Operators" in perlop for more
2485 details.
2486 Note drivers are free to avoid the overhead of creating an DBI
2488 statement handle for do(), especially if there are no parameters. In
2489 this case error handlers, if invoked during do(), will be passed the
2490 database handle.
2491 "last_insert_id"
2493 $rv = $dbh->last_insert_id();
2495 $rv = $dbh->last_insert_id($catalog, $schema, $table, $field);
2496 $rv = $dbh->last_insert_id($catalog, $schema, $table, $field, \%attr);
2497 Returns a value 'identifying' the row just inserted, if possible.
2499 Typically this would be a value assigned by the database server to a
2500 column with an auto_increment or serial type. Returns undef if the
2501 driver does not support the method or can't determine the value.
2502 The $catalog, $schema, $table, and $field parameters may be required
2504 for some drivers (see below). If you don't know the parameter values
2505 and your driver does not need them, then use "undef" for each.
2506 There are several caveats to be aware of with this method if you want
2508 to use it for portable applications:
2509 * For some drivers the value may only available immediately after the
2511 insert statement has executed (e.g., mysql, Informix).
2512 * For some drivers the $catalog, $schema, $table, and $field parameters
2514 are required, for others they are ignored (e.g., mysql).
2515 * Drivers may return an indeterminate value if no insert has been
2517 performed yet.
2518 * For some drivers the value may only be available if placeholders have
2520 not been used (e.g., Sybase, MS SQL). In this case the value returned
2521 would be from the last non-placeholder insert statement.
2522 * Some drivers may need driver-specific hints about how to get the
2524 value. For example, being told the name of the database 'sequence'
2525 object that holds the value. Any such hints are passed as driver-
2526 specific attributes in the \%attr parameter.
2527 * If the underlying database offers nothing better, then some drivers
2529 may attempt to implement this method by executing ""select max($field)
2530 from $table"". Drivers using any approach like this should issue a
2531 warning if "AutoCommit" is true because it is generally unsafe -
2532 another process may have modified the table between your insert and the
2533 select. For situations where you know it is safe, such as when you have
2534 locked the table, you can silence the warning by passing "Warn" => 0 in
2535 \%attr.
2536 * If no insert has been performed yet, or the last insert failed, then
2538 the value is implementation defined.
2539 Given all the caveats above, it's clear that this method must be used
2541 with care.
2542 The "last_insert_id" method was added in DBI 1.38.
2544 "selectrow_array"
2546 @row_ary = $dbh->selectrow_array($statement);
2548 @row_ary = $dbh->selectrow_array($statement, \%attr);
2549 @row_ary = $dbh->selectrow_array($statement, \%attr, @bind_values);
2550 This utility method combines "prepare", "execute" and "fetchrow_array"
2552 into a single call. If called in a list context, it returns the first
2553 row of data from the statement. The $statement parameter can be a
2554 previously prepared statement handle, in which case the "prepare" is
2555 skipped.
2556 If any method fails, and "RaiseError" is not set, "selectrow_array"
2558 will return an empty list.
2559 If called in a scalar context for a statement handle that has more than
2561 one column, it is undefined whether the driver will return the value of
2562 the first column or the last. So don't do that. Also, in a scalar
2563 context, an "undef" is returned if there are no more rows or if an
2564 error occurred. That "undef" can't be distinguished from an "undef"
2565 returned because the first field value was NULL. For these reasons you
2566 should exercise some caution if you use "selectrow_array" in a scalar
2567 context, or just don't do that.
2568 "selectrow_arrayref"
2570 $ary_ref = $dbh->selectrow_arrayref($statement);
2572 $ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
2573 $ary_ref = $dbh->selectrow_arrayref($statement, \%attr, @bind_values);
2574 This utility method combines "prepare", "execute" and
2576 "fetchrow_arrayref" into a single call. It returns the first row of
2577 data from the statement. The $statement parameter can be a previously
2578 prepared statement handle, in which case the "prepare" is skipped.
2579 If any method fails, and "RaiseError" is not set, "selectrow_arrayref"
2581 will return undef.
2582 "selectrow_hashref"
2584 $hash_ref = $dbh->selectrow_hashref($statement);
2586 $hash_ref = $dbh->selectrow_hashref($statement, \%attr);
2587 $hash_ref = $dbh->selectrow_hashref($statement, \%attr, @bind_values);
2588 This utility method combines "prepare", "execute" and
2590 "fetchrow_hashref" into a single call. It returns the first row of data
2591 from the statement. The $statement parameter can be a previously
2592 prepared statement handle, in which case the "prepare" is skipped.
2593 If any method fails, and "RaiseError" is not set, "selectrow_hashref"
2595 will return undef.
2596 "selectall_arrayref"
2598 $ary_ref = $dbh->selectall_arrayref($statement);
2600 $ary_ref = $dbh->selectall_arrayref($statement, \%attr);
2601 $ary_ref = $dbh->selectall_arrayref($statement, \%attr, @bind_values);
2602 This utility method combines "prepare", "execute" and
2604 "fetchall_arrayref" into a single call. It returns a reference to an
2605 array containing a reference to an array (or hash, see below) for each
2606 row of data fetched.
2607 The $statement parameter can be a previously prepared statement handle,
2609 in which case the "prepare" is skipped. This is recommended if the
2610 statement is going to be executed many times.
2611 If "RaiseError" is not set and any method except "fetchall_arrayref"
2613 fails then "selectall_arrayref" will return "undef"; if
2614 "fetchall_arrayref" fails then it will return with whatever data has
2615 been fetched thus far. You should check "$dbh->err" afterwards (or use
2616 the "RaiseError" attribute) to discover if the data is complete or was
2617 truncated due to an error.
2618 The "fetchall_arrayref" method called by "selectall_arrayref" supports
2620 a $max_rows parameter. You can specify a value for $max_rows by
2621 including a '"MaxRows"' attribute in \%attr. In which case finish() is
2622 called for you after fetchall_arrayref() returns.
2623 The "fetchall_arrayref" method called by "selectall_arrayref" also
2625 supports a $slice parameter. You can specify a value for $slice by
2626 including a '"Slice"' or '"Columns"' attribute in \%attr. The only
2627 difference between the two is that if "Slice" is not defined and
2628 "Columns" is an array ref, then the array is assumed to contain column
2629 index values (which count from 1), rather than perl array index values.
2630 In which case the array is copied and each value decremented before
2631 passing to "/fetchall_arrayref".
2632 You may often want to fetch an array of rows where each row is stored
2634 as a hash. That can be done simply using:
2635 my $emps = $dbh->selectall_arrayref(
2637 "SELECT ename FROM emp ORDER BY ename",
2638 { Slice => {} }
2639 );
2640 foreach my $emp ( @$emps ) {
2641 print "Employee: $emp->{ename}\n";
2642 }
2643 Or, to fetch into an array instead of an array ref:
2645 @result = @{ $dbh->selectall_arrayref($sql, { Slice => {} }) };
2647 See "fetchall_arrayref" method for more details.
2649 "selectall_array"
2651 @ary = $dbh->selectall_array($statement);
2653 @ary = $dbh->selectall_array($statement, \%attr);
2654 @ary = $dbh->selectall_array($statement, \%attr, @bind_values);
2655 This is a convenience wrapper around selectall_arrayref that returns
2657 the rows directly as a list, rather than a reference to an array of
2658 rows.
2659 Note that if "RaiseError" is not set then you can't tell the difference
2661 between returning no rows and an error. Using RaiseError is best
2662 practice.
2663 "selectall_hashref"
2665 $hash_ref = $dbh->selectall_hashref($statement, $key_field);
2667 $hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr);
2668 $hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr, @bind_values);
2669 This utility method combines "prepare", "execute" and
2671 "fetchall_hashref" into a single call. It returns a reference to a hash
2672 containing one entry, at most, for each row, as returned by
2673 fetchall_hashref().
2674 The $statement parameter can be a previously prepared statement handle,
2676 in which case the "prepare" is skipped. This is recommended if the
2677 statement is going to be executed many times.
2678 The $key_field parameter defines which column, or columns, are used as
2680 keys in the returned hash. It can either be the name of a single field,
2681 or a reference to an array containing multiple field names. Using
2682 multiple names yields a tree of nested hashes.
2683 If a row has the same key as an earlier row then it replaces the
2685 earlier row.
2686 If any method except "fetchall_hashref" fails, and "RaiseError" is not
2688 set, "selectall_hashref" will return "undef". If "fetchall_hashref"
2689 fails and "RaiseError" is not set, then it will return with whatever
2690 data it has fetched thus far. $DBI::err should be checked to catch
2691 that.
2692 See fetchall_hashref() for more details.
2694 "selectcol_arrayref"
2696 $ary_ref = $dbh->selectcol_arrayref($statement);
2698 $ary_ref = $dbh->selectcol_arrayref($statement, \%attr);
2699 $ary_ref = $dbh->selectcol_arrayref($statement, \%attr, @bind_values);
2700 This utility method combines "prepare", "execute", and fetching one
2702 column from all the rows, into a single call. It returns a reference to
2703 an array containing the values of the first column from each row.
2704 The $statement parameter can be a previously prepared statement handle,
2706 in which case the "prepare" is skipped. This is recommended if the
2707 statement is going to be executed many times.
2708 If any method except "fetch" fails, and "RaiseError" is not set,
2710 "selectcol_arrayref" will return "undef". If "fetch" fails and
2711 "RaiseError" is not set, then it will return with whatever data it has
2712 fetched thus far. $DBI::err should be checked to catch that.
2713 The "selectcol_arrayref" method defaults to pushing a single column
2715 value (the first) from each row into the result array. However, it can
2716 also push another column, or even multiple columns per row, into the
2717 result array. This behaviour can be specified via a '"Columns"'
2718 attribute which must be a ref to an array containing the column number
2719 or numbers to use. For example:
2720 # get array of id and name pairs:
2722 my $ary_ref = $dbh->selectcol_arrayref("select id, name from table", { Columns=>[1,2] });
2723 my %hash = @$ary_ref; # build hash from key-value pairs so $hash{$id} => name
2724 You can specify a maximum number of rows to fetch by including a
2726 '"MaxRows"' attribute in \%attr.
2727 "prepare"
2729 $sth = $dbh->prepare($statement) or die $dbh->errstr;
2731 $sth = $dbh->prepare($statement, \%attr) or die $dbh->errstr;
2732 Prepares a statement for later execution by the database engine and
2734 returns a reference to a statement handle object.
2735 The returned statement handle can be used to get attributes of the
2737 statement and invoke the "execute" method. See "Statement Handle
2738 Methods".
2739 Drivers for engines without the concept of preparing a statement will
2741 typically just store the statement in the returned handle and process
2742 it when "$sth->execute" is called. Such drivers are unlikely to give
2743 much useful information about the statement, such as
2744 "$sth->{NUM_OF_FIELDS}", until after "$sth->execute" has been called.
2745 Portable applications should take this into account.
2746 In general, DBI drivers do not parse the contents of the statement
2748 (other than simply counting any Placeholders). The statement is passed
2749 directly to the database engine, sometimes known as pass-thru mode.
2750 This has advantages and disadvantages. On the plus side, you can access
2751 all the functionality of the engine being used. On the downside, you're
2752 limited if you're using a simple engine, and you need to take extra
2753 care if writing applications intended to be portable between engines.
2754 Portable applications should not assume that a new statement can be
2756 prepared and/or executed while still fetching results from a previous
2757 statement.
2758 Some command-line SQL tools use statement terminators, like a
2760 semicolon, to indicate the end of a statement. Such terminators should
2761 not normally be used with the DBI.
2762 "prepare_cached"
2764 $sth = $dbh->prepare_cached($statement)
2766 $sth = $dbh->prepare_cached($statement, \%attr)
2767 $sth = $dbh->prepare_cached($statement, \%attr, $if_active)
2768 Like "prepare" except that the statement handle returned will be stored
2770 in a hash associated with the $dbh. If another call is made to
2771 "prepare_cached" with the same $statement and %attr parameter values,
2772 then the corresponding cached $sth will be returned without contacting
2773 the database server. Be sure to understand the cautions and caveats
2774 noted below.
2775 The $if_active parameter lets you adjust the behaviour if an already
2777 cached statement handle is still Active. There are several
2778 alternatives:
2779 0: A warning will be generated, and finish() will be called on the
2781 statement handle before it is returned. This is the default behaviour
2782 if $if_active is not passed.
2783 1: finish() will be called on the statement handle, but the warning is
2784 suppressed.
2785 2: Disables any checking.
2786 3: The existing active statement handle will be removed from the cache
2787 and a new statement handle prepared and cached in its place. This is
2788 the safest option because it doesn't affect the state of the old
2789 handle, it just removes it from the cache. [Added in DBI 1.40]
2790 Here are some examples of "prepare_cached":
2792 sub insert_hash {
2794 my ($table, $field_values) = @_;
2795 # sort to keep field order, and thus sql, stable for prepare_cached
2796 my @fields = sort keys %$field_values;
2797 my @values = @{$field_values}{@fields};
2798 my $sql = sprintf "insert into %s (%s) values (%s)",
2799 $table, join(",", @fields), join(",", ("?")x@fields);
2800 my $sth = $dbh->prepare_cached($sql);
2801 return $sth->execute(@values);
2802 }
2803 sub search_hash {
2805 my ($table, $field_values) = @_;
2806 # sort to keep field order, and thus sql, stable for prepare_cached
2807 my @fields = sort keys %$field_values;
2808 my @values = @{$field_values}{@fields};
2809 my $qualifier = "";
2810 $qualifier = "where ".join(" and ", map { "$_=?" } @fields) if @fields;
2811 $sth = $dbh->prepare_cached("SELECT * FROM $table $qualifier");
2812 return $dbh->selectall_arrayref($sth, {}, @values);
2813 }
2814 Caveat emptor: This caching can be useful in some applications, but it
2816 can also cause problems and should be used with care. Here is a
2817 contrived case where caching would cause a significant problem:
2818 my $sth = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
2820 $sth->execute(...);
2821 while (my $data = $sth->fetchrow_hashref) {
2822 # later, in some other code called within the loop...
2824 my $sth2 = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
2825 $sth2->execute(...);
2826 while (my $data2 = $sth2->fetchrow_arrayref) {
2827 do_stuff(...);
2828 }
2829 }
2830 In this example, since both handles are preparing the exact same
2832 statement, $sth2 will not be its own statement handle, but a duplicate
2833 of $sth returned from the cache. The results will certainly not be what
2834 you expect. Typically the inner fetch loop will work normally,
2835 fetching all the records and terminating when there are no more, but
2836 now that $sth is the same as $sth2 the outer fetch loop will also
2837 terminate.
2838 You'll know if you run into this problem because prepare_cached() will
2840 generate a warning by default (when $if_active is false).
2841 The cache used by prepare_cached() is keyed by both the statement and
2843 any attributes so you can also avoid this issue by doing something
2844 like:
2845 $sth = $dbh->prepare_cached("...", { dbi_dummy => __FILE__.__LINE__ });
2847 which will ensure that prepare_cached only returns statements cached by
2849 that line of code in that source file.
2850 Also, to ensure the attributes passed are always the same, avoid
2852 passing references inline. For example, the Slice attribute is
2853 specified as a reference. Be sure to declare it external to the call to
2854 prepare_cached(), such that a new hash reference is not created on
2855 every call. See "connect_cached" for more details and examples.
2856 If you'd like the cache to managed intelligently, you can tie the
2858 hashref returned by "CachedKids" to an appropriate caching module, such
2859 as Tie::Cache::LRU:
2860 my $cache;
2862 tie %$cache, 'Tie::Cache::LRU', 500;
2863 $dbh->{CachedKids} = $cache;
2864 "commit"
2866 $rc = $dbh->commit or die $dbh->errstr;
2868 Commit (make permanent) the most recent series of database changes if
2870 the database supports transactions and AutoCommit is off.
2871 If "AutoCommit" is on, then calling "commit" will issue a "commit
2873 ineffective with AutoCommit" warning.
2874 See also "Transactions" in the "FURTHER INFORMATION" section below.
2876 "rollback"
2878 $rc = $dbh->rollback or die $dbh->errstr;
2880 Rollback (undo) the most recent series of uncommitted database changes
2882 if the database supports transactions and AutoCommit is off.
2883 If "AutoCommit" is on, then calling "rollback" will issue a "rollback
2885 ineffective with AutoCommit" warning.
2886 See also "Transactions" in the "FURTHER INFORMATION" section below.
2888 "begin_work"
2890 $rc = $dbh->begin_work or die $dbh->errstr;
2892 Enable transactions (by turning "AutoCommit" off) until the next call
2894 to "commit" or "rollback". After the next "commit" or "rollback",
2895 "AutoCommit" will automatically be turned on again.
2896 If "AutoCommit" is already off when "begin_work" is called then it does
2898 nothing except return an error. If the driver does not support
2899 transactions then when "begin_work" attempts to set "AutoCommit" off
2900 the driver will trigger a fatal error.
2901 See also "Transactions" in the "FURTHER INFORMATION" section below.
2903 "disconnect"
2905 $rc = $dbh->disconnect or warn $dbh->errstr;
2907 Disconnects the database from the database handle. "disconnect" is
2909 typically only used before exiting the program. The handle is of little
2910 use after disconnecting.
2911 The transaction behaviour of the "disconnect" method is, sadly,
2913 undefined. Some database systems (such as Oracle and Ingres) will
2914 automatically commit any outstanding changes, but others (such as
2915 Informix) will rollback any outstanding changes. Applications not
2916 using "AutoCommit" should explicitly call "commit" or "rollback" before
2917 calling "disconnect".
2918 The database is automatically disconnected by the "DESTROY" method if
2920 still connected when there are no longer any references to the handle.
2921 The "DESTROY" method for each driver should implicitly call "rollback"
2922 to undo any uncommitted changes. This is vital behaviour to ensure that
2923 incomplete transactions don't get committed simply because Perl calls
2924 "DESTROY" on every object before exiting. Also, do not rely on the
2925 order of object destruction during "global destruction", as it is
2926 undefined.
2927 Generally, if you want your changes to be committed or rolled back when
2929 you disconnect, then you should explicitly call "commit" or "rollback"
2930 before disconnecting.
2931 If you disconnect from a database while you still have active statement
2933 handles (e.g., SELECT statement handles that may have more data to
2934 fetch), you will get a warning. The warning may indicate that a fetch
2935 loop terminated early, perhaps due to an uncaught error. To avoid the
2936 warning call the "finish" method on the active handles.
2937 "ping"
2939 $rc = $dbh->ping;
2941 Attempts to determine, in a reasonably efficient way, if the database
2943 server is still running and the connection to it is still working.
2944 Individual drivers should implement this function in the most suitable
2945 manner for their database engine.
2946 The current default implementation always returns true without actually
2948 doing anything. Actually, it returns ""0 but true"" which is true but
2949 zero. That way you can tell if the return value is genuine or just the
2950 default. Drivers should override this method with one that does the
2951 right thing for their type of database.
2952 Few applications would have direct use for this method. See the
2954 specialized Apache::DBI module for one example usage.
2955 "get_info"
2957 $value = $dbh->get_info( $info_type );
2959 Returns information about the implementation, i.e. driver and data
2961 source capabilities, restrictions etc. It returns "undef" for unknown
2962 or unimplemented information types. For example:
2963 $database_version = $dbh->get_info( 18 ); # SQL_DBMS_VER
2965 $max_select_tables = $dbh->get_info( 106 ); # SQL_MAXIMUM_TABLES_IN_SELECT
2966 See "Standards Reference Information" for more detailed information
2968 about the information types and their meanings and possible return
2969 values.
2970 The DBI::Const::GetInfoType module exports a %GetInfoType hash that can
2972 be used to map info type names to numbers. For example:
2973 $database_version = $dbh->get_info( $GetInfoType{SQL_DBMS_VER} );
2975 The names are a merging of the ANSI and ODBC standards (which differ in
2977 some cases). See DBI::Const::GetInfoType for more details.
2978 Because some DBI methods make use of get_info(), drivers are strongly
2980 encouraged to support at least the following very minimal set of
2981 information types to ensure the DBI itself works properly:
2982 Type Name Example A Example B
2984 ---- -------------------------- ------------ ----------------
2985 17 SQL_DBMS_NAME 'ACCESS' 'Oracle'
2986 18 SQL_DBMS_VER '03.50.0000' '08.01.0721 ...'
2987 29 SQL_IDENTIFIER_QUOTE_CHAR '`' '"'
2988 41 SQL_CATALOG_NAME_SEPARATOR '.' '@'
2989 114 SQL_CATALOG_LOCATION 1 2
2990 Values from 9000 to 9999 for get_info are officially reserved for use
2992 by Perl DBI. Values in that range which have been assigned a meaning
2993 are defined here:
2994 9000: true if a backslash character ("\") before placeholder-like text
2996 (e.g. "?", ":foo") will prevent it being treated as a placeholder by
2997 the driver. The backslash will be removed before the text is passed to
2998 the backend.
2999 "table_info"
3001 $sth = $dbh->table_info( $catalog, $schema, $table, $type );
3003 $sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );
3004 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3006 Returns an active statement handle that can be used to fetch
3008 information about tables and views that exist in the database.
3009 The arguments $catalog, $schema and $table may accept search patterns
3011 according to the database/driver, for example: $table = '%FOO%';
3012 Remember that the underscore character ('"_"') is a search pattern that
3013 means match any character, so 'FOO_%' is the same as 'FOO%' and
3014 'FOO_BAR%' will match names like 'FOO1BAR'.
3015 The value of $type is a comma-separated list of one or more types of
3017 tables to be returned in the result set. Each value may optionally be
3018 quoted, e.g.:
3019 $type = "TABLE";
3021 $type = "'TABLE','VIEW'";
3022 In addition the following special cases may also be supported by some
3024 drivers:
3025 · If the value of $catalog is '%' and $schema and $table name are
3027 empty strings, the result set contains a list of catalog names.
3028 For example:
3029 $sth = $dbh->table_info('%', '', '');
3031 · If the value of $schema is '%' and $catalog and $table are empty
3033 strings, the result set contains a list of schema names.
3034 · If the value of $type is '%' and $catalog, $schema, and $table are
3036 all empty strings, the result set contains a list of table types.
3037 If your driver doesn't support one or more of the selection filter
3039 parameters then you may get back more than you asked for and can do the
3040 filtering yourself.
3041 This method can be expensive, and can return a large amount of data.
3043 (For example, small Oracle installation returns over 2000 rows.) So
3044 it's a good idea to use the filters to limit the data as much as
3045 possible.
3046 The statement handle returned has at least the following fields in the
3048 order show below. Other fields, after these, may also be present.
3049 TABLE_CAT: Table catalog identifier. This field is NULL ("undef") if
3051 not applicable to the data source, which is usually the case. This
3052 field is empty if not applicable to the table.
3053 TABLE_SCHEM: The name of the schema containing the TABLE_NAME value.
3055 This field is NULL ("undef") if not applicable to data source, and
3056 empty if not applicable to the table.
3057 TABLE_NAME: Name of the table (or view, synonym, etc).
3059 TABLE_TYPE: One of the following: "TABLE", "VIEW", "SYSTEM TABLE",
3061 "GLOBAL TEMPORARY", "LOCAL TEMPORARY", "ALIAS", "SYNONYM" or a type
3062 identifier that is specific to the data source.
3063 REMARKS: A description of the table. May be NULL ("undef").
3065 Note that "table_info" might not return records for all tables.
3067 Applications can use any valid table regardless of whether it's
3068 returned by "table_info".
3069 See also "tables", "Catalog Methods" and "Standards Reference
3071 Information".
3072 "column_info"
3074 $sth = $dbh->column_info( $catalog, $schema, $table, $column );
3076 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3078 Returns an active statement handle that can be used to fetch
3080 information about columns in specified tables.
3081 The arguments $schema, $table and $column may accept search patterns
3083 according to the database/driver, for example: $table = '%FOO%';
3084 Note: The support for the selection criteria is driver specific. If the
3086 driver doesn't support one or more of them then you may get back more
3087 than you asked for and can do the filtering yourself.
3088 Note: If your driver does not support column_info an undef is returned.
3090 This is distinct from asking for something which does not exist in a
3091 driver which supports column_info as a valid statement handle to an
3092 empty result-set will be returned in this case.
3093 If the arguments don't match any tables then you'll still get a
3095 statement handle, it'll just return no rows.
3096 The statement handle returned has at least the following fields in the
3098 order shown below. Other fields, after these, may also be present.
3099 TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not
3101 applicable to the data source, which is often the case. This field is
3102 empty if not applicable to the table.
3103 TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if
3105 not applicable to the data source, and empty if not applicable to the
3106 table.
3107 TABLE_NAME: The table identifier. Note: A driver may provide column
3109 metadata not only for base tables, but also for derived objects like
3110 SYNONYMS etc.
3111 COLUMN_NAME: The column identifier.
3113 DATA_TYPE: The concise data type code.
3115 TYPE_NAME: A data source dependent data type name.
3117 COLUMN_SIZE: The column size. This is the maximum length in characters
3119 for character data types, the number of digits or bits for numeric data
3120 types or the length in the representation of temporal types. See the
3121 relevant specifications for detailed information.
3122 BUFFER_LENGTH: The length in bytes of transferred data.
3124 DECIMAL_DIGITS: The total number of significant digits to the right of
3126 the decimal point.
3127 NUM_PREC_RADIX: The radix for numeric precision. The value is 10 or 2
3129 for numeric data types and NULL ("undef") if not applicable.
3130 NULLABLE: Indicates if a column can accept NULLs. The following values
3132 are defined:
3133 SQL_NO_NULLS 0
3135 SQL_NULLABLE 1
3136 SQL_NULLABLE_UNKNOWN 2
3137 REMARKS: A description of the column.
3139 COLUMN_DEF: The default value of the column, in a format that can be
3141 used directly in an SQL statement.
3142 Note that this may be an expression and not simply the text used for
3144 the default value in the original CREATE TABLE statement. For example,
3145 given:
3146 col1 char(30) default current_user -- a 'function'
3148 col2 char(30) default 'string' -- a string literal
3149 where "current_user" is the name of a function, the corresponding
3151 "COLUMN_DEF" values would be:
3152 Database col1 col2
3154 -------- ---- ----
3155 Oracle: current_user 'string'
3156 Postgres: "current_user"() 'string'::text
3157 MS SQL: (user_name()) ('string')
3158 SQL_DATA_TYPE: The SQL data type.
3160 SQL_DATETIME_SUB: The subtype code for datetime and interval data
3162 types.
3163 CHAR_OCTET_LENGTH: The maximum length in bytes of a character or binary
3165 data type column.
3166 ORDINAL_POSITION: The column sequence number (starting with 1).
3168 IS_NULLABLE: Indicates if the column can accept NULLs. Possible values
3170 are: 'NO', 'YES' and ''.
3171 SQL/CLI defines the following additional columns:
3173 CHAR_SET_CAT
3175 CHAR_SET_SCHEM
3176 CHAR_SET_NAME
3177 COLLATION_CAT
3178 COLLATION_SCHEM
3179 COLLATION_NAME
3180 UDT_CAT
3181 UDT_SCHEM
3182 UDT_NAME
3183 DOMAIN_CAT
3184 DOMAIN_SCHEM
3185 DOMAIN_NAME
3186 SCOPE_CAT
3187 SCOPE_SCHEM
3188 SCOPE_NAME
3189 MAX_CARDINALITY
3190 DTD_IDENTIFIER
3191 IS_SELF_REF
3192 Drivers capable of supplying any of those values should do so in the
3194 corresponding column and supply undef values for the others.
3195 Drivers wishing to provide extra database/driver specific information
3197 should do so in extra columns beyond all those listed above, and use
3198 lowercase field names with the driver-specific prefix (i.e.,
3199 'ora_...'). Applications accessing such fields should do so by name and
3200 not by column number.
3201 The result set is ordered by TABLE_CAT, TABLE_SCHEM, TABLE_NAME and
3203 ORDINAL_POSITION.
3204 Note: There is some overlap with statement handle attributes (in perl)
3206 and SQLDescribeCol (in ODBC). However, SQLColumns provides more
3207 metadata.
3208 See also "Catalog Methods" and "Standards Reference Information".
3210 "primary_key_info"
3212 $sth = $dbh->primary_key_info( $catalog, $schema, $table );
3214 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3216 Returns an active statement handle that can be used to fetch
3218 information about columns that make up the primary key for a table.
3219 The arguments don't accept search patterns (unlike table_info()).
3220 The statement handle will return one row per column, ordered by
3222 TABLE_CAT, TABLE_SCHEM, TABLE_NAME, and KEY_SEQ. If there is no
3223 primary key then the statement handle will fetch no rows.
3224 Note: The support for the selection criteria, such as $catalog, is
3226 driver specific. If the driver doesn't support catalogs and/or
3227 schemas, it may ignore these criteria.
3228 The statement handle returned has at least the following fields in the
3230 order shown below. Other fields, after these, may also be present.
3231 TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not
3233 applicable to the data source, which is often the case. This field is
3234 empty if not applicable to the table.
3235 TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if
3237 not applicable to the data source, and empty if not applicable to the
3238 table.
3239 TABLE_NAME: The table identifier.
3241 COLUMN_NAME: The column identifier.
3243 KEY_SEQ: The column sequence number (starting with 1). Note: This
3245 field is named ORDINAL_POSITION in SQL/CLI.
3246 PK_NAME: The primary key constraint identifier. This field is NULL
3248 ("undef") if not applicable to the data source.
3249 See also "Catalog Methods" and "Standards Reference Information".
3251 "primary_key"
3253 @key_column_names = $dbh->primary_key( $catalog, $schema, $table );
3255 Simple interface to the primary_key_info() method. Returns a list of
3257 the column names that comprise the primary key of the specified table.
3258 The list is in primary key column sequence order. If there is no
3259 primary key then an empty list is returned.
3260 "foreign_key_info"
3262 $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
3264 , $fk_catalog, $fk_schema, $fk_table );
3265 $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
3267 , $fk_catalog, $fk_schema, $fk_table
3268 , \%attr );
3269 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3271 Returns an active statement handle that can be used to fetch
3273 information about foreign keys in and/or referencing the specified
3274 table(s). The arguments don't accept search patterns (unlike
3275 table_info()).
3276 $pk_catalog, $pk_schema, $pk_table identify the primary (unique) key
3278 table (PKT).
3279 $fk_catalog, $fk_schema, $fk_table identify the foreign key table
3281 (FKT).
3282 If both PKT and FKT are given, the function returns the foreign key, if
3284 any, in table FKT that refers to the primary (unique) key of table PKT.
3285 (Note: In SQL/CLI, the result is implementation-defined.)
3286 If only PKT is given, then the result set contains the primary key of
3288 that table and all foreign keys that refer to it.
3289 If only FKT is given, then the result set contains all foreign keys in
3291 that table and the primary keys to which they refer. (Note: In
3292 SQL/CLI, the result includes unique keys too.)
3293 For example:
3295 $sth = $dbh->foreign_key_info( undef, $user, 'master');
3297 $sth = $dbh->foreign_key_info( undef, undef, undef , undef, $user, 'detail');
3298 $sth = $dbh->foreign_key_info( undef, $user, 'master', undef, $user, 'detail');
3299 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3301 Note: The support for the selection criteria, such as $catalog, is
3303 driver specific. If the driver doesn't support catalogs and/or
3304 schemas, it may ignore these criteria.
3305 The statement handle returned has the following fields in the order
3307 shown below. Because ODBC never includes unique keys, they define
3308 different columns in the result set than SQL/CLI. SQL/CLI column names
3309 are shown in parentheses.
3310 PKTABLE_CAT ( UK_TABLE_CAT ): The primary (unique) key table
3312 catalog identifier. This field is NULL ("undef") if not applicable to
3313 the data source, which is often the case. This field is empty if not
3314 applicable to the table.
3315 PKTABLE_SCHEM ( UK_TABLE_SCHEM ): The primary (unique) key table
3317 schema identifier. This field is NULL ("undef") if not applicable to
3318 the data source, and empty if not applicable to the table.
3319 PKTABLE_NAME ( UK_TABLE_NAME ): The primary (unique) key table
3321 identifier.
3322 PKCOLUMN_NAME (UK_COLUMN_NAME ): The primary (unique) key column
3324 identifier.
3325 FKTABLE_CAT ( FK_TABLE_CAT ): The foreign key table catalog
3327 identifier. This field is NULL ("undef") if not applicable to the data
3328 source, which is often the case. This field is empty if not applicable
3329 to the table.
3330 FKTABLE_SCHEM ( FK_TABLE_SCHEM ): The foreign key table schema
3332 identifier. This field is NULL ("undef") if not applicable to the data
3333 source, and empty if not applicable to the table.
3334 FKTABLE_NAME ( FK_TABLE_NAME ): The foreign key table identifier.
3336 FKCOLUMN_NAME ( FK_COLUMN_NAME ): The foreign key column
3338 identifier.
3339 KEY_SEQ ( ORDINAL_POSITION ): The column sequence number
3341 (starting with 1).
3342 UPDATE_RULE ( UPDATE_RULE ): The referential action for the
3344 UPDATE rule. The following codes are defined:
3345 CASCADE 0
3347 RESTRICT 1
3348 SET NULL 2
3349 NO ACTION 3
3350 SET DEFAULT 4
3351 DELETE_RULE ( DELETE_RULE ): The referential action for the
3353 DELETE rule. The codes are the same as for UPDATE_RULE.
3354 FK_NAME ( FK_NAME ): The foreign key name.
3356 PK_NAME ( UK_NAME ): The primary (unique) key name.
3358 DEFERRABILITY ( DEFERABILITY ): The deferrability of the foreign
3360 key constraint. The following codes are defined:
3361 INITIALLY DEFERRED 5
3363 INITIALLY IMMEDIATE 6
3364 NOT DEFERRABLE 7
3365 ( UNIQUE_OR_PRIMARY ): This column is necessary if a
3367 driver includes all candidate (i.e. primary and alternate) keys in the
3368 result set (as specified by SQL/CLI). The value of this column is
3369 UNIQUE if the foreign key references an alternate key and PRIMARY if
3370 the foreign key references a primary key, or it may be undefined if the
3371 driver doesn't have access to the information.
3372 See also "Catalog Methods" and "Standards Reference Information".
3374 "statistics_info"
3376 Warning: This method is experimental and may change.
3378 $sth = $dbh->statistics_info( $catalog, $schema, $table, $unique_only, $quick );
3380 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3382 Returns an active statement handle that can be used to fetch
3384 statistical information about a table and its indexes.
3385 The arguments don't accept search patterns (unlike "table_info").
3387 If the boolean argument $unique_only is true, only UNIQUE indexes will
3389 be returned in the result set, otherwise all indexes will be returned.
3390 If the boolean argument $quick is set, the actual statistical
3392 information columns (CARDINALITY and PAGES) will only be returned if
3393 they are readily available from the server, and might not be current.
3394 Some databases may return stale statistics or no statistics at all with
3395 this flag set.
3396 The statement handle will return at most one row per column name per
3398 index, plus at most one row for the entire table itself, ordered by
3399 NON_UNIQUE, TYPE, INDEX_QUALIFIER, INDEX_NAME, and ORDINAL_POSITION.
3400 Note: The support for the selection criteria, such as $catalog, is
3402 driver specific. If the driver doesn't support catalogs and/or
3403 schemas, it may ignore these criteria.
3404 The statement handle returned has at least the following fields in the
3406 order shown below. Other fields, after these, may also be present.
3407 TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not
3409 applicable to the data source, which is often the case. This field is
3410 empty if not applicable to the table.
3411 TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if
3413 not applicable to the data source, and empty if not applicable to the
3414 table.
3415 TABLE_NAME: The table identifier.
3417 NON_UNIQUE: Unique index indicator. Returns 0 for unique indexes, 1
3419 for non-unique indexes
3420 INDEX_QUALIFIER: Index qualifier identifier. The identifier that is
3422 used to qualify the index name when doing a "DROP INDEX"; NULL
3423 ("undef") is returned if an index qualifier is not supported by the
3424 data source. If a non-NULL (defined) value is returned in this column,
3425 it must be used to qualify the index name on a "DROP INDEX" statement;
3426 otherwise, the TABLE_SCHEM should be used to qualify the index name.
3427 INDEX_NAME: The index identifier.
3429 TYPE: The type of information being returned. Can be any of the
3431 following values: 'table', 'btree', 'clustered', 'content', 'hashed',
3432 or 'other'.
3433 In the case that this field is 'table', all fields other than
3435 TABLE_CAT, TABLE_SCHEM, TABLE_NAME, TYPE, CARDINALITY, and PAGES will
3436 be NULL ("undef").
3437 ORDINAL_POSITION: Column sequence number (starting with 1).
3439 COLUMN_NAME: The column identifier.
3441 ASC_OR_DESC: Column sort sequence. "A" for Ascending, "D" for
3443 Descending, or NULL ("undef") if not supported for this index.
3444 CARDINALITY: Cardinality of the table or index. For indexes, this is
3446 the number of unique values in the index. For tables, this is the
3447 number of rows in the table. If not supported, the value will be NULL
3448 ("undef").
3449 PAGES: Number of storage pages used by this table or index. If not
3451 supported, the value will be NULL ("undef").
3452 FILTER_CONDITION: The index filter condition as a string. If the index
3454 is not a filtered index, or it cannot be determined whether the index
3455 is a filtered index, this value is NULL ("undef"). If the index is a
3456 filtered index, but the filter condition cannot be determined, this
3457 value is the empty string ''. Otherwise it will be the literal filter
3458 condition as a string, such as "SALARY <= 4500".
3459 See also "Catalog Methods" and "Standards Reference Information".
3461 "tables"
3463 @names = $dbh->tables( $catalog, $schema, $table, $type );
3465 @names = $dbh->tables; # deprecated
3466 Simple interface to table_info(). Returns a list of matching table
3468 names, possibly including a catalog/schema prefix.
3469 See "table_info" for a description of the parameters.
3471 If "$dbh->get_info(29)" returns true (29 is SQL_IDENTIFIER_QUOTE_CHAR)
3473 then the table names are constructed and quoted by "quote_identifier"
3474 to ensure they are usable even if they contain whitespace or reserved
3475 words etc. This means that the table names returned will include quote
3476 characters.
3477 "type_info_all"
3479 $type_info_all = $dbh->type_info_all;
3481 Returns a reference to an array which holds information about each data
3483 type variant supported by the database and driver. The array and its
3484 contents should be treated as read-only.
3485 The first item is a reference to an 'index' hash of "Name ="> "Index"
3487 pairs. The items following that are references to arrays, one per
3488 supported data type variant. The leading index hash defines the names
3489 and order of the fields within the arrays that follow it. For example:
3490 $type_info_all = [
3492 { TYPE_NAME => 0,
3493 DATA_TYPE => 1,
3494 COLUMN_SIZE => 2, # was PRECISION originally
3495 LITERAL_PREFIX => 3,
3496 LITERAL_SUFFIX => 4,
3497 CREATE_PARAMS => 5,
3498 NULLABLE => 6,
3499 CASE_SENSITIVE => 7,
3500 SEARCHABLE => 8,
3501 UNSIGNED_ATTRIBUTE=> 9,
3502 FIXED_PREC_SCALE => 10, # was MONEY originally
3503 AUTO_UNIQUE_VALUE => 11, # was AUTO_INCREMENT originally
3504 LOCAL_TYPE_NAME => 12,
3505 MINIMUM_SCALE => 13,
3506 MAXIMUM_SCALE => 14,
3507 SQL_DATA_TYPE => 15,
3508 SQL_DATETIME_SUB => 16,
3509 NUM_PREC_RADIX => 17,
3510 INTERVAL_PRECISION=> 18,
3511 },
3512 [ 'VARCHAR', SQL_VARCHAR,
3513 undef, "'","'", undef,0, 1,1,0,0,0,undef,1,255, undef
3514 ],
3515 [ 'INTEGER', SQL_INTEGER,
3516 undef, "", "", undef,0, 0,1,0,0,0,undef,0, 0, 10
3517 ],
3518 ];
3519 More than one row may have the same value in the "DATA_TYPE" field if
3521 there are different ways to spell the type name and/or there are
3522 variants of the type with different attributes (e.g., with and without
3523 "AUTO_UNIQUE_VALUE" set, with and without "UNSIGNED_ATTRIBUTE", etc).
3524 The rows are ordered by "DATA_TYPE" first and then by how closely each
3526 type maps to the corresponding ODBC SQL data type, closest first.
3527 The meaning of the fields is described in the documentation for the
3529 "type_info" method.
3530 An 'index' hash is provided so you don't need to rely on index values
3532 defined above. However, using DBD::ODBC with some old ODBC drivers may
3533 return older names, shown as comments in the example above. Another
3534 issue with the index hash is that the lettercase of the keys is not
3535 defined. It is usually uppercase, as show here, but drivers may return
3536 names with any lettercase.
3537 Drivers are also free to return extra driver-specific columns of
3539 information - though it's recommended that they start at column index
3540 50 to leave room for expansion of the DBI/ODBC specification.
3541 The type_info_all() method is not normally used directly. The
3543 "type_info" method provides a more usable and useful interface to the
3544 data.
3545 "type_info"
3547 @type_info = $dbh->type_info($data_type);
3549 Returns a list of hash references holding information about one or more
3551 variants of $data_type. The list is ordered by "DATA_TYPE" first and
3552 then by how closely each type maps to the corresponding ODBC SQL data
3553 type, closest first. If called in a scalar context then only the first
3554 (best) element is returned.
3555 If $data_type is undefined or "SQL_ALL_TYPES", then the list will
3557 contain hashes for all data type variants supported by the database and
3558 driver.
3559 If $data_type is an array reference then "type_info" returns the
3561 information for the first type in the array that has any matches.
3562 The keys of the hash follow the same letter case conventions as the
3564 rest of the DBI (see "Naming Conventions and Name Space"). The
3565 following uppercase items should always exist, though may be undef:
3566 TYPE_NAME (string)
3568 Data type name for use in CREATE TABLE statements etc.
3569 DATA_TYPE (integer)
3571 SQL data type number.
3572 COLUMN_SIZE (integer)
3574 For numeric types, this is either the total number of digits (if
3575 the NUM_PREC_RADIX value is 10) or the total number of bits allowed
3576 in the column (if NUM_PREC_RADIX is 2).
3577 For string types, this is the maximum size of the string in
3579 characters.
3580 For date and interval types, this is the maximum number of
3582 characters needed to display the value.
3583 LITERAL_PREFIX (string)
3585 Characters used to prefix a literal. A typical prefix is ""'"" for
3586 characters, or possibly ""0x"" for binary values passed as
3587 hexadecimal. NULL ("undef") is returned for data types for which
3588 this is not applicable.
3589 LITERAL_SUFFIX (string)
3591 Characters used to suffix a literal. Typically ""'"" for
3592 characters. NULL ("undef") is returned for data types where this
3593 is not applicable.
3594 CREATE_PARAMS (string)
3596 Parameter names for data type definition. For example,
3597 "CREATE_PARAMS" for a "DECIMAL" would be ""precision,scale"" if the
3598 DECIMAL type should be declared as "DECIMAL("precision,scale")"
3599 where precision and scale are integer values. For a "VARCHAR" it
3600 would be ""max length"". NULL ("undef") is returned for data types
3601 for which this is not applicable.
3602 NULLABLE (integer)
3604 Indicates whether the data type accepts a NULL value: 0 or an empty
3605 string = no, 1 = yes, 2 = unknown.
3606 CASE_SENSITIVE (boolean)
3608 Indicates whether the data type is case sensitive in collations and
3609 comparisons.
3610 SEARCHABLE (integer)
3612 Indicates how the data type can be used in a WHERE clause, as
3613 follows:
3614 0 - Cannot be used in a WHERE clause
3616 1 - Only with a LIKE predicate
3617 2 - All comparison operators except LIKE
3618 3 - Can be used in a WHERE clause with any comparison operator
3619 UNSIGNED_ATTRIBUTE (boolean)
3621 Indicates whether the data type is unsigned. NULL ("undef") is
3622 returned for data types for which this is not applicable.
3623 FIXED_PREC_SCALE (boolean)
3625 Indicates whether the data type always has the same precision and
3626 scale (such as a money type). NULL ("undef") is returned for data
3627 types for which this is not applicable.
3628 AUTO_UNIQUE_VALUE (boolean)
3630 Indicates whether a column of this data type is automatically set
3631 to a unique value whenever a new row is inserted. NULL ("undef")
3632 is returned for data types for which this is not applicable.
3633 LOCAL_TYPE_NAME (string)
3635 Localized version of the "TYPE_NAME" for use in dialog with users.
3636 NULL ("undef") is returned if a localized name is not available (in
3637 which case "TYPE_NAME" should be used).
3638 MINIMUM_SCALE (integer)
3640 The minimum scale of the data type. If a data type has a fixed
3641 scale, then "MAXIMUM_SCALE" holds the same value. NULL ("undef")
3642 is returned for data types for which this is not applicable.
3643 MAXIMUM_SCALE (integer)
3645 The maximum scale of the data type. If a data type has a fixed
3646 scale, then "MINIMUM_SCALE" holds the same value. NULL ("undef")
3647 is returned for data types for which this is not applicable.
3648 SQL_DATA_TYPE (integer)
3650 This column is the same as the "DATA_TYPE" column, except for
3651 interval and datetime data types. For interval and datetime data
3652 types, the "SQL_DATA_TYPE" field will return "SQL_INTERVAL" or
3653 "SQL_DATETIME", and the "SQL_DATETIME_SUB" field below will return
3654 the subcode for the specific interval or datetime data type. If
3655 this field is NULL, then the driver does not support or report on
3656 interval or datetime subtypes.
3657 SQL_DATETIME_SUB (integer)
3659 For interval or datetime data types, where the "SQL_DATA_TYPE"
3660 field above is "SQL_INTERVAL" or "SQL_DATETIME", this field will
3661 hold the subcode for the specific interval or datetime data type.
3662 Otherwise it will be NULL ("undef").
3663 Although not mentioned explicitly in the standards, it seems there
3665 is a simple relationship between these values:
3666 DATA_TYPE == (10 * SQL_DATA_TYPE) + SQL_DATETIME_SUB
3668 NUM_PREC_RADIX (integer)
3670 The radix value of the data type. For approximate numeric types,
3671 "NUM_PREC_RADIX" contains the value 2 and "COLUMN_SIZE" holds the
3672 number of bits. For exact numeric types, "NUM_PREC_RADIX" contains
3673 the value 10 and "COLUMN_SIZE" holds the number of decimal digits.
3674 NULL ("undef") is returned either for data types for which this is
3675 not applicable or if the driver cannot report this information.
3676 INTERVAL_PRECISION (integer)
3678 The interval leading precision for interval types. NULL is returned
3679 either for data types for which this is not applicable or if the
3680 driver cannot report this information.
3681 For example, to find the type name for the fields in a select statement
3683 you can do:
3684 @names = map { scalar $dbh->type_info($_)->{TYPE_NAME} } @{ $sth->{TYPE} }
3686 Since DBI and ODBC drivers vary in how they map their types into the
3688 ISO standard types you may need to search for more than one type.
3689 Here's an example looking for a usable type to store a date:
3690 $my_date_type = $dbh->type_info( [ SQL_DATE, SQL_TIMESTAMP ] );
3692 Similarly, to more reliably find a type to store small integers, you
3694 could use a list starting with "SQL_SMALLINT", "SQL_INTEGER",
3695 "SQL_DECIMAL", etc.
3696 See also "Standards Reference Information".
3698 "quote"
3700 $sql = $dbh->quote($value);
3702 $sql = $dbh->quote($value, $data_type);
3703 Quote a string literal for use as a literal value in an SQL statement,
3705 by escaping any special characters (such as quotation marks) contained
3706 within the string and adding the required type of outer quotation
3707 marks.
3708 $sql = sprintf "SELECT foo FROM bar WHERE baz = %s",
3710 $dbh->quote("Don't");
3711 For most database types, at least those that conform to SQL standards,
3713 quote would return 'Don''t' (including the outer quotation marks). For
3714 others it may return something like 'Don\'t'
3715 An undefined $value value will be returned as the string "NULL"
3717 (without single quotation marks) to match how NULLs are represented in
3718 SQL.
3719 If $data_type is supplied, it is used to try to determine the required
3721 quoting behaviour by using the information returned by "type_info". As
3722 a special case, the standard numeric types are optimized to return
3723 $value without calling "type_info".
3724 Quote will probably not be able to deal with all possible input (such
3726 as binary data or data containing newlines), and is not related in any
3727 way with escaping or quoting shell meta-characters.
3728 It is valid for the quote() method to return an SQL expression that
3730 evaluates to the desired string. For example:
3731 $quoted = $dbh->quote("one\ntwo\0three")
3733 may return something like:
3735 CONCAT('one', CHAR(12), 'two', CHAR(0), 'three')
3737 The quote() method should not be used with "Placeholders and Bind
3739 Values".
3740 "quote_identifier"
3742 $sql = $dbh->quote_identifier( $name );
3744 $sql = $dbh->quote_identifier( $catalog, $schema, $table, \%attr );
3745 Quote an identifier (table name etc.) for use in an SQL statement, by
3747 escaping any special characters (such as double quotation marks) it
3748 contains and adding the required type of outer quotation marks.
3749 Undefined names are ignored and the remainder are quoted and then
3751 joined together, typically with a dot (".") character. For example:
3752 $id = $dbh->quote_identifier( undef, 'Her schema', 'My table' );
3754 would, for most database types, return "Her schema"."My table"
3756 (including all the double quotation marks).
3757 If three names are supplied then the first is assumed to be a catalog
3759 name and special rules may be applied based on what "get_info" returns
3760 for SQL_CATALOG_NAME_SEPARATOR (41) and SQL_CATALOG_LOCATION (114).
3761 For example, for Oracle:
3762 $id = $dbh->quote_identifier( 'link', 'schema', 'table' );
3764 would return "schema"."table"@"link".
3766 "take_imp_data"
3768 $imp_data = $dbh->take_imp_data;
3770 Leaves the $dbh in an almost dead, zombie-like, state and returns a
3772 binary string of raw implementation data from the driver which
3773 describes the current database connection. Effectively it detaches the
3774 underlying database API connection data from the DBI handle. After
3775 calling take_imp_data(), all other methods except "DESTROY" will
3776 generate a warning and return undef.
3777 Why would you want to do this? You don't, forget I even mentioned it.
3779 Unless, that is, you're implementing something advanced like a multi-
3780 threaded connection pool. See DBI::Pool.
3781 The returned $imp_data can be passed as a "dbi_imp_data" attribute to a
3783 later connect() call, even in a separate thread in the same process,
3784 where the driver can use it to 'adopt' the existing connection that the
3785 implementation data was taken from.
3786 Some things to keep in mind...
3788 * the $imp_data holds the only reference to the underlying database API
3790 connection data. That connection is still 'live' and won't be cleaned
3791 up properly unless the $imp_data is used to create a new $dbh which is
3792 then allowed to disconnect() normally.
3793 * using the same $imp_data to create more than one other new $dbh at a
3795 time may well lead to unpleasant problems. Don't do that.
3796 Any child statement handles are effectively destroyed when
3798 take_imp_data() is called.
3799 The "take_imp_data" method was added in DBI 1.36 but wasn't useful till
3801 1.49.
3802 Database Handle Attributes
3804 This section describes attributes specific to database handles.
3805 Changes to these database handle attributes do not affect any other
3807 existing or future database handles.
3808 Attempting to set or get the value of an unknown attribute generates a
3810 warning, except for private driver-specific attributes (which all have
3811 names starting with a lowercase letter).
3812 Example:
3814 $h->{AutoCommit} = ...; # set/write
3816 ... = $h->{AutoCommit}; # get/read
3817 "AutoCommit"
3819 Type: boolean
3821 If true, then database changes cannot be rolled-back (undone). If
3823 false, then database changes automatically occur within a
3824 "transaction", which must either be committed or rolled back using the
3825 "commit" or "rollback" methods.
3826 Drivers should always default to "AutoCommit" mode (an unfortunate
3828 choice largely forced on the DBI by ODBC and JDBC conventions.)
3829 Attempting to set "AutoCommit" to an unsupported value is a fatal
3831 error. This is an important feature of the DBI. Applications that need
3832 full transaction behaviour can set "$dbh->{AutoCommit} = 0" (or set
3833 "AutoCommit" to 0 via "connect") without having to check that the value
3834 was assigned successfully.
3835 For the purposes of this description, we can divide databases into
3837 three categories:
3838 Databases which don't support transactions at all.
3840 Databases in which a transaction is always active.
3841 Databases in which a transaction must be explicitly started (C<'BEGIN WORK'>).
3842 * Databases which don't support transactions at all
3844 For these databases, attempting to turn "AutoCommit" off is a fatal
3846 error. "commit" and "rollback" both issue warnings about being
3847 ineffective while "AutoCommit" is in effect.
3848 * Databases in which a transaction is always active
3850 These are typically mainstream commercial relational databases with
3852 "ANSI standard" transaction behaviour. If "AutoCommit" is off, then
3853 changes to the database won't have any lasting effect unless "commit"
3854 is called (but see also "disconnect"). If "rollback" is called then any
3855 changes since the last commit are undone.
3856 If "AutoCommit" is on, then the effect is the same as if the DBI called
3858 "commit" automatically after every successful database operation. So
3859 calling "commit" or "rollback" explicitly while "AutoCommit" is on
3860 would be ineffective because the changes would have already been
3861 committed.
3862 Changing "AutoCommit" from off to on will trigger a "commit".
3864 For databases which don't support a specific auto-commit mode, the
3866 driver has to commit each statement automatically using an explicit
3867 "COMMIT" after it completes successfully (and roll it back using an
3868 explicit "ROLLBACK" if it fails). The error information reported to
3869 the application will correspond to the statement which was executed,
3870 unless it succeeded and the commit or rollback failed.
3871 * Databases in which a transaction must be explicitly started
3873 For these databases, the intention is to have them act like databases
3875 in which a transaction is always active (as described above).
3876 To do this, the driver will automatically begin an explicit transaction
3878 when "AutoCommit" is turned off, or after a "commit" or "rollback" (or
3879 when the application issues the next database operation after one of
3880 those events).
3881 In this way, the application does not have to treat these databases as
3883 a special case.
3884 See "commit", "disconnect" and "Transactions" for other important notes
3886 about transactions.
3887 "Driver"
3889 Type: handle
3891 Holds the handle of the parent driver. The only recommended use for
3893 this is to find the name of the driver using:
3894 $dbh->{Driver}->{Name}
3896 "Name"
3898 Type: string
3900 Holds the "name" of the database. Usually (and recommended to be) the
3902 same as the ""dbi:DriverName:..."" string used to connect to the
3903 database, but with the leading ""dbi:DriverName:"" removed.
3904 "Statement"
3906 Type: string, read-only
3908 Returns the statement string passed to the most recent "prepare" or
3910 "do" method called in this database handle, even if that method failed.
3911 This is especially useful where "RaiseError" is enabled and the
3912 exception handler checks $@ and sees that a 'prepare' method call
3913 failed.
3914 "RowCacheSize"
3916 Type: integer
3918 A hint to the driver indicating the size of the local row cache that
3920 the application would like the driver to use for future "SELECT"
3921 statements. If a row cache is not implemented, then setting
3922 "RowCacheSize" is ignored and getting the value returns "undef".
3923 Some "RowCacheSize" values have special meaning, as follows:
3925 0 - Automatically determine a reasonable cache size for each C<SELECT>
3927 1 - Disable the local row cache
3928 >1 - Cache this many rows
3929 <0 - Cache as many rows that will fit into this much memory for each C<SELECT>.
3930 Note that large cache sizes may require a very large amount of memory
3932 (cached rows * maximum size of row). Also, a large cache will cause a
3933 longer delay not only for the first fetch, but also whenever the cache
3934 needs refilling.
3935 See also the "RowsInCache" statement handle attribute.
3937 "Username"
3939 Type: string
3941 Returns the username used to connect to the database.
3943
3945 This section lists the methods and attributes associated with DBI
3946 statement handles.
3947 Statement Handle Methods
3949 The DBI defines the following methods for use on DBI statement handles:
3950 "bind_param"
3952 $sth->bind_param($p_num, $bind_value)
3954 $sth->bind_param($p_num, $bind_value, \%attr)
3955 $sth->bind_param($p_num, $bind_value, $bind_type)
3956 The "bind_param" method takes a copy of $bind_value and associates it
3958 (binds it) with a placeholder, identified by $p_num, embedded in the
3959 prepared statement. Placeholders are indicated with question mark
3960 character ("?"). For example:
3961 $dbh->{RaiseError} = 1; # save having to check each method call
3963 $sth = $dbh->prepare("SELECT name, age FROM people WHERE name LIKE ?");
3964 $sth->bind_param(1, "John%"); # placeholders are numbered from 1
3965 $sth->execute;
3966 DBI::dump_results($sth);
3967 See "Placeholders and Bind Values" for more information.
3969 Data Types for Placeholders
3971 The "\%attr" parameter can be used to hint at the data type the
3973 placeholder should have. This is rarely needed. Typically, the driver
3974 is only interested in knowing if the placeholder should be bound as a
3975 number or a string.
3976 $sth->bind_param(1, $value, { TYPE => SQL_INTEGER });
3978 As a short-cut for the common case, the data type can be passed
3980 directly, in place of the "\%attr" hash reference. This example is
3981 equivalent to the one above:
3982 $sth->bind_param(1, $value, SQL_INTEGER);
3984 The "TYPE" value indicates the standard (non-driver-specific) type for
3986 this parameter. To specify the driver-specific type, the driver may
3987 support a driver-specific attribute, such as "{ ora_type => 97 }".
3988 The SQL_INTEGER and other related constants can be imported using
3990 use DBI qw(:sql_types);
3992 See "DBI Constants" for more information.
3994 The data type is 'sticky' in that bind values passed to execute() are
3996 bound with the data type specified by earlier bind_param() calls, if
3997 any. Portable applications should not rely on being able to change the
3998 data type after the first "bind_param" call.
3999 Perl only has string and number scalar data types. All database types
4001 that aren't numbers are bound as strings and must be in a format the
4002 database will understand except where the bind_param() TYPE attribute
4003 specifies a type that implies a particular format. For example, given:
4004 $sth->bind_param(1, $value, SQL_DATETIME);
4006 the driver should expect $value to be in the ODBC standard SQL_DATETIME
4008 format, which is 'YYYY-MM-DD HH:MM:SS'. Similarly for SQL_DATE,
4009 SQL_TIME etc.
4010 As an alternative to specifying the data type in the "bind_param" call,
4012 you can let the driver pass the value as the default type ("VARCHAR").
4013 You can then use an SQL function to convert the type within the
4014 statement. For example:
4015 INSERT INTO price(code, price) VALUES (?, CONVERT(MONEY,?))
4017 The "CONVERT" function used here is just an example. The actual
4019 function and syntax will vary between different databases and is non-
4020 portable.
4021 See also "Placeholders and Bind Values" for more information.
4023 "bind_param_inout"
4025 $rc = $sth->bind_param_inout($p_num, \$bind_value, $max_len) or die $sth->errstr;
4027 $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, \%attr) or ...
4028 $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, $bind_type) or ...
4029 This method acts like "bind_param", but also enables values to be
4031 updated by the statement. The statement is typically a call to a stored
4032 procedure. The $bind_value must be passed as a reference to the actual
4033 value to be used.
4034 Note that unlike "bind_param", the $bind_value variable is not copied
4036 when "bind_param_inout" is called. Instead, the value in the variable
4037 is read at the time "execute" is called.
4038 The additional $max_len parameter specifies the minimum amount of
4040 memory to allocate to $bind_value for the new value. If the value
4041 returned from the database is too big to fit, then the execution should
4042 fail. If unsure what value to use, pick a generous length, i.e., a
4043 length larger than the longest value that would ever be returned. The
4044 only cost of using a larger value than needed is wasted memory.
4045 Undefined values or "undef" are used to indicate null values. See also
4047 "Placeholders and Bind Values" for more information.
4048 "bind_param_array"
4050 $rc = $sth->bind_param_array($p_num, $array_ref_or_value)
4052 $rc = $sth->bind_param_array($p_num, $array_ref_or_value, \%attr)
4053 $rc = $sth->bind_param_array($p_num, $array_ref_or_value, $bind_type)
4054 The "bind_param_array" method is used to bind an array of values to a
4056 placeholder embedded in the prepared statement which is to be executed
4057 with "execute_array". For example:
4058 $dbh->{RaiseError} = 1; # save having to check each method call
4060 $sth = $dbh->prepare("INSERT INTO staff (first_name, last_name, dept) VALUES(?, ?, ?)");
4061 $sth->bind_param_array(1, [ 'John', 'Mary', 'Tim' ]);
4062 $sth->bind_param_array(2, [ 'Booth', 'Todd', 'Robinson' ]);
4063 $sth->bind_param_array(3, "SALES"); # scalar will be reused for each row
4064 $sth->execute_array( { ArrayTupleStatus => \my @tuple_status } );
4065 The %attr ($bind_type) argument is the same as defined for
4067 "bind_param". Refer to "bind_param" for general details on using
4068 placeholders.
4069 (Note that bind_param_array() can not be used to expand a placeholder
4071 into a list of values for a statement like "SELECT foo WHERE bar IN
4072 (?)". A placeholder can only ever represent one value per execution.)
4073 Scalar values, including "undef", may also be bound by
4075 "bind_param_array". In which case the same value will be used for each
4076 "execute" call. Driver-specific implementations may behave differently,
4077 e.g., when binding to a stored procedure call, some databases may
4078 permit mixing scalars and arrays as arguments.
4079 The default implementation provided by DBI (for drivers that have not
4081 implemented array binding) is to iteratively call "execute" for each
4082 parameter tuple provided in the bound arrays. Drivers may provide more
4083 optimized implementations using whatever bulk operation support the
4084 database API provides. The default driver behaviour should match the
4085 default DBI behaviour, but always consult your driver documentation as
4086 there may be driver specific issues to consider.
4087 Note that the default implementation currently only supports non-data
4089 returning statements (INSERT, UPDATE, but not SELECT). Also,
4090 "bind_param_array" and "bind_param" cannot be mixed in the same
4091 statement execution, and "bind_param_array" must be used with
4092 "execute_array"; using "bind_param_array" will have no effect for
4093 "execute".
4094 The "bind_param_array" method was added in DBI 1.22.
4096 "execute"
4098 $rv = $sth->execute or die $sth->errstr;
4100 $rv = $sth->execute(@bind_values) or die $sth->errstr;
4101 Perform whatever processing is necessary to execute the prepared
4103 statement. An "undef" is returned if an error occurs. A successful
4104 "execute" always returns true regardless of the number of rows
4105 affected, even if it's zero (see below). It is always important to
4106 check the return status of "execute" (and most other DBI methods) for
4107 errors if you're not using "RaiseError".
4108 For a non-"SELECT" statement, "execute" returns the number of rows
4110 affected, if known. If no rows were affected, then "execute" returns
4111 "0E0", which Perl will treat as 0 but will regard as true. Note that it
4112 is not an error for no rows to be affected by a statement. If the
4113 number of rows affected is not known, then "execute" returns -1.
4114 For "SELECT" statements, execute simply "starts" the query within the
4116 database engine. Use one of the fetch methods to retrieve the data
4117 after calling "execute". The "execute" method does not return the
4118 number of rows that will be returned by the query (because most
4119 databases can't tell in advance), it simply returns a true value.
4120 You can tell if the statement was a "SELECT" statement by checking if
4122 "$sth->{NUM_OF_FIELDS}" is greater than zero after calling "execute".
4123 If any arguments are given, then "execute" will effectively call
4125 "bind_param" for each value before executing the statement. Values
4126 bound in this way are usually treated as "SQL_VARCHAR" types unless the
4127 driver can determine the correct type (which is rare), or unless
4128 "bind_param" (or "bind_param_inout") has already been used to specify
4129 the type.
4130 Note that passing "execute" an empty array is the same as passing no
4132 arguments at all, which will execute the statement with previously
4133 bound values. That's probably not what you want.
4134 If execute() is called on a statement handle that's still active
4136 ($sth->{Active} is true) then it should effectively call finish() to
4137 tidy up the previous execution results before starting this new
4138 execution.
4139 "execute_array"
4141 $tuples = $sth->execute_array(\%attr) or die $sth->errstr;
4143 $tuples = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
4144 ($tuples, $rows) = $sth->execute_array(\%attr) or die $sth->errstr;
4146 ($tuples, $rows) = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
4147 Execute the prepared statement once for each parameter tuple (group of
4149 values) provided either in the @bind_values, or by prior calls to
4150 "bind_param_array", or via a reference passed in \%attr.
4151 When called in scalar context the execute_array() method returns the
4153 number of tuples executed, or "undef" if an error occurred. Like
4154 execute(), a successful execute_array() always returns true regardless
4155 of the number of tuples executed, even if it's zero. If there were any
4156 errors the ArrayTupleStatus array can be used to discover which tuples
4157 failed and with what errors.
4158 When called in list context the execute_array() method returns two
4160 scalars; $tuples is the same as calling execute_array() in scalar
4161 context and $rows is the number of rows affected for each tuple, if
4162 available or -1 if the driver cannot determine this. NOTE, some drivers
4163 cannot determine the number of rows affected per tuple but can provide
4164 the number of rows affected for the batch. If you are doing an update
4165 operation the returned rows affected may not be what you expect if, for
4166 instance, one or more of the tuples affected the same row multiple
4167 times. Some drivers may not yet support list context, in which case
4168 $rows will be undef, or may not be able to provide the number of rows
4169 affected when performing this batch operation, in which case $rows will
4170 be -1.
4171 Bind values for the tuples to be executed may be supplied row-wise by
4173 an "ArrayTupleFetch" attribute, or else column-wise in the @bind_values
4174 argument, or else column-wise by prior calls to "bind_param_array".
4175 Where column-wise binding is used (via the @bind_values argument or
4177 calls to bind_param_array()) the maximum number of elements in any one
4178 of the bound value arrays determines the number of tuples executed.
4179 Placeholders with fewer values in their parameter arrays are treated as
4180 if padded with undef (NULL) values.
4181 If a scalar value is bound, instead of an array reference, it is
4183 treated as a variable length array with all elements having the same
4184 value. It does not influence the number of tuples executed, so if all
4185 bound arrays have zero elements then zero tuples will be executed. If
4186 all bound values are scalars then one tuple will be executed, making
4187 execute_array() act just like execute().
4188 The "ArrayTupleFetch" attribute can be used to specify a reference to a
4190 subroutine that will be called to provide the bind values for each
4191 tuple execution. The subroutine should return an reference to an array
4192 which contains the appropriate number of bind values, or return an
4193 undef if there is no more data to execute.
4194 As a convenience, the "ArrayTupleFetch" attribute can also be used to
4196 specify a statement handle. In which case the fetchrow_arrayref()
4197 method will be called on the given statement handle in order to provide
4198 the bind values for each tuple execution.
4199 The values specified via bind_param_array() or the @bind_values
4201 parameter may be either scalars, or arrayrefs. If any @bind_values are
4202 given, then "execute_array" will effectively call "bind_param_array"
4203 for each value before executing the statement. Values bound in this
4204 way are usually treated as "SQL_VARCHAR" types unless the driver can
4205 determine the correct type (which is rare), or unless "bind_param",
4206 "bind_param_inout", "bind_param_array", or "bind_param_inout_array" has
4207 already been used to specify the type. See "bind_param_array" for
4208 details.
4209 The "ArrayTupleStatus" attribute can be used to specify a reference to
4211 an array which will receive the execute status of each executed
4212 parameter tuple. Note the "ArrayTupleStatus" attribute was mandatory
4213 until DBI 1.38.
4214 For tuples which are successfully executed, the element at the same
4216 ordinal position in the status array is the resulting rowcount (or -1
4217 if unknown). If the execution of a tuple causes an error, then the
4218 corresponding status array element will be set to a reference to an
4219 array containing "err", "errstr" and "state" set by the failed
4220 execution.
4221 If any tuple execution returns an error, "execute_array" will return
4223 "undef". In that case, the application should inspect the status array
4224 to determine which parameter tuples failed. Some databases may not
4225 continue executing tuples beyond the first failure. In this case the
4226 status array will either hold fewer elements, or the elements beyond
4227 the failure will be undef.
4228 If all parameter tuples are successfully executed, "execute_array"
4230 returns the number tuples executed. If no tuples were executed, then
4231 execute_array() returns "0E0", just like execute() does, which Perl
4232 will treat as 0 but will regard as true.
4233 For example:
4235 $sth = $dbh->prepare("INSERT INTO staff (first_name, last_name) VALUES (?, ?)");
4237 my $tuples = $sth->execute_array(
4238 { ArrayTupleStatus => \my @tuple_status },
4239 \@first_names,
4240 \@last_names,
4241 );
4242 if ($tuples) {
4243 print "Successfully inserted $tuples records\n";
4244 }
4245 else {
4246 for my $tuple (0..@last_names-1) {
4247 my $status = $tuple_status[$tuple];
4248 $status = [0, "Skipped"] unless defined $status;
4249 next unless ref $status;
4250 printf "Failed to insert (%s, %s): %s\n",
4251 $first_names[$tuple], $last_names[$tuple], $status->[1];
4252 }
4253 }
4254 Support for data returning statements such as SELECT is driver-specific
4256 and subject to change. At present, the default implementation provided
4257 by DBI only supports non-data returning statements.
4258 Transaction semantics when using array binding are driver and database
4260 specific. If "AutoCommit" is on, the default DBI implementation will
4261 cause each parameter tuple to be individually committed (or rolled back
4262 in the event of an error). If "AutoCommit" is off, the application is
4263 responsible for explicitly committing the entire set of bound parameter
4264 tuples. Note that different drivers and databases may have different
4265 behaviours when some parameter tuples cause failures. In some cases,
4266 the driver or database may automatically rollback the effect of all
4267 prior parameter tuples that succeeded in the transaction; other drivers
4268 or databases may retain the effect of prior successfully executed
4269 parameter tuples. Be sure to check your driver and database for its
4270 specific behaviour.
4271 Note that, in general, performance will usually be better with
4273 "AutoCommit" turned off, and using explicit "commit" after each
4274 "execute_array" call.
4275 The "execute_array" method was added in DBI 1.22, and ArrayTupleFetch
4277 was added in 1.36.
4278 "execute_for_fetch"
4280 $tuples = $sth->execute_for_fetch($fetch_tuple_sub);
4282 $tuples = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
4283 ($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub);
4285 ($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
4286 The execute_for_fetch() method is used to perform bulk operations and
4288 although it is most often used via the execute_array() method you can
4289 use it directly. The main difference between execute_array and
4290 execute_for_fetch is the former does column or row-wise binding and the
4291 latter uses row-wise binding.
4292 The fetch subroutine, referenced by $fetch_tuple_sub, is expected to
4294 return a reference to an array (known as a 'tuple') or undef.
4295 The execute_for_fetch() method calls $fetch_tuple_sub, without any
4297 parameters, until it returns a false value. Each tuple returned is used
4298 to provide bind values for an $sth->execute(@$tuple) call.
4299 In scalar context execute_for_fetch() returns "undef" if there were any
4301 errors and the number of tuples executed otherwise. Like execute() and
4302 execute_array() a zero is returned as "0E0" so execute_for_fetch() is
4303 only false on error. If there were any errors the @tuple_status array
4304 can be used to discover which tuples failed and with what errors.
4305 When called in list context execute_for_fetch() returns two scalars;
4307 $tuples is the same as calling execute_for_fetch() in scalar context
4308 and $rows is the sum of the number of rows affected for each tuple, if
4309 available or -1 if the driver cannot determine this. If you are doing
4310 an update operation the returned rows affected may not be what you
4311 expect if, for instance, one or more of the tuples affected the same
4312 row multiple times. Some drivers may not yet support list context, in
4313 which case $rows will be undef, or may not be able to provide the
4314 number of rows affected when performing this batch operation, in which
4315 case $rows will be -1.
4316 If \@tuple_status is passed then the execute_for_fetch method uses it
4318 to return status information. The tuple_status array holds one element
4319 per tuple. If the corresponding execute() did not fail then the element
4320 holds the return value from execute(), which is typically a row count.
4321 If the execute() did fail then the element holds a reference to an
4322 array containing ($sth->err, $sth->errstr, $sth->state).
4323 If the driver detects an error that it knows means no further tuples
4325 can be executed then it may return, with an error status, even though
4326 $fetch_tuple_sub may still have more tuples to be executed.
4327 Although each tuple returned by $fetch_tuple_sub is effectively used to
4329 call $sth->execute(@$tuple_array_ref) the exact timing may vary.
4330 Drivers are free to accumulate sets of tuples to pass to the database
4331 server in bulk group operations for more efficient execution. However,
4332 the $fetch_tuple_sub is specifically allowed to return the same array
4333 reference each time (which is what fetchrow_arrayref() usually does).
4334 For example:
4336 my $sel = $dbh1->prepare("select foo, bar from table1");
4338 $sel->execute;
4339 my $ins = $dbh2->prepare("insert into table2 (foo, bar) values (?,?)");
4341 my $fetch_tuple_sub = sub { $sel->fetchrow_arrayref };
4342 my @tuple_status;
4344 $rc = $ins->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
4345 my @errors = grep { ref $_ } @tuple_status;
4346 Similarly, if you already have an array containing the data rows to be
4348 processed you'd use a subroutine to shift off and return each array ref
4349 in turn:
4350 $ins->execute_for_fetch( sub { shift @array_of_arrays }, \@tuple_status);
4352 The "execute_for_fetch" method was added in DBI 1.38.
4354 "last_insert_id"
4356 $rv = $sth->last_insert_id();
4358 $rv = $sth->last_insert_id($catalog, $schema, $table, $field);
4359 $rv = $sth->last_insert_id($catalog, $schema, $table, $field, \%attr);
4360 Returns a value 'identifying' the row inserted by last execution of the
4362 statement $sth, if possible.
4363 For some drivers the value may be 'identifying' the row inserted by the
4365 last executed statement, not by $sth.
4366 See database handle method last_insert_id for all details.
4368 The "last_insert_id" statement method was added in DBI 1.642.
4370 "fetchrow_arrayref"
4372 $ary_ref = $sth->fetchrow_arrayref;
4374 $ary_ref = $sth->fetch; # alias
4375 Fetches the next row of data and returns a reference to an array
4377 holding the field values. Null fields are returned as "undef" values
4378 in the array. This is the fastest way to fetch data, particularly if
4379 used with "$sth->bind_columns".
4380 If there are no more rows or if an error occurs, then
4382 "fetchrow_arrayref" returns an "undef". You should check "$sth->err"
4383 afterwards (or use the "RaiseError" attribute) to discover if the
4384 "undef" returned was due to an error.
4385 Note that the same array reference is returned for each fetch, so don't
4387 store the reference and then use it after a later fetch. Also, the
4388 elements of the array are also reused for each row, so take care if you
4389 want to take a reference to an element. See also "bind_columns".
4390 "fetchrow_array"
4392 @ary = $sth->fetchrow_array;
4394 An alternative to "fetchrow_arrayref". Fetches the next row of data and
4396 returns it as a list containing the field values. Null fields are
4397 returned as "undef" values in the list.
4398 If there are no more rows or if an error occurs, then "fetchrow_array"
4400 returns an empty list. You should check "$sth->err" afterwards (or use
4401 the "RaiseError" attribute) to discover if the empty list returned was
4402 due to an error.
4403 If called in a scalar context for a statement handle that has more than
4405 one column, it is undefined whether the driver will return the value of
4406 the first column or the last. So don't do that. Also, in a scalar
4407 context, an "undef" is returned if there are no more rows or if an
4408 error occurred. That "undef" can't be distinguished from an "undef"
4409 returned because the first field value was NULL. For these reasons you
4410 should exercise some caution if you use "fetchrow_array" in a scalar
4411 context.
4412 "fetchrow_hashref"
4414 $hash_ref = $sth->fetchrow_hashref;
4416 $hash_ref = $sth->fetchrow_hashref($name);
4417 An alternative to "fetchrow_arrayref". Fetches the next row of data and
4419 returns it as a reference to a hash containing field name and field
4420 value pairs. Null fields are returned as "undef" values in the hash.
4421 If there are no more rows or if an error occurs, then
4423 "fetchrow_hashref" returns an "undef". You should check "$sth->err"
4424 afterwards (or use the "RaiseError" attribute) to discover if the
4425 "undef" returned was due to an error.
4426 The optional $name parameter specifies the name of the statement handle
4428 attribute. For historical reasons it defaults to ""NAME"", however
4429 using either ""NAME_lc"" or ""NAME_uc"" is recommended for portability.
4430 The keys of the hash are the same names returned by "$sth->{$name}". If
4432 more than one field has the same name, there will only be one entry in
4433 the returned hash for those fields, so statements like ""select foo,
4434 foo from bar"" will return only a single key from "fetchrow_hashref".
4435 In these cases use column aliases or "fetchrow_arrayref". Note that it
4436 is the database server (and not the DBD implementation) which provides
4437 the name for fields containing functions like "count(*)" or
4438 ""max(c_foo)"" and they may clash with existing column names (most
4439 databases don't care about duplicate column names in a result-set). If
4440 you want these to return as unique names that are the same across
4441 databases, use aliases, as in ""select count(*) as cnt"" or ""select
4442 max(c_foo) mx_foo, ..."" depending on the syntax your database
4443 supports.
4444 Because of the extra work "fetchrow_hashref" and Perl have to perform,
4446 it is not as efficient as "fetchrow_arrayref" or "fetchrow_array".
4447 By default a reference to a new hash is returned for each row. It is
4449 likely that a future version of the DBI will support an attribute which
4450 will enable the same hash to be reused for each row. This will give a
4451 significant performance boost, but it won't be enabled by default
4452 because of the risk of breaking old code.
4453 "fetchall_arrayref"
4455 $tbl_ary_ref = $sth->fetchall_arrayref;
4457 $tbl_ary_ref = $sth->fetchall_arrayref( $slice );
4458 $tbl_ary_ref = $sth->fetchall_arrayref( $slice, $max_rows );
4459 The "fetchall_arrayref" method can be used to fetch all the data to be
4461 returned from a prepared and executed statement handle. It returns a
4462 reference to an array that contains one reference per row.
4463 If called on an inactive statement handle, "fetchall_arrayref" returns
4465 undef.
4466 If there are no rows left to return from an active statement handle,
4468 "fetchall_arrayref" returns a reference to an empty array. If an error
4469 occurs, "fetchall_arrayref" returns the data fetched thus far, which
4470 may be none. You should check "$sth->err" afterwards (or use the
4471 "RaiseError" attribute) to discover if the data is complete or was
4472 truncated due to an error.
4473 If $slice is an array reference, "fetchall_arrayref" uses
4475 "fetchrow_arrayref" to fetch each row as an array ref. If the $slice
4476 array is not empty then it is used as a slice to select individual
4477 columns by perl array index number (starting at 0, unlike column and
4478 parameter numbers which start at 1).
4479 With no parameters, or if $slice is undefined, "fetchall_arrayref" acts
4481 as if passed an empty array ref.
4482 For example, to fetch just the first column of every row:
4484 $tbl_ary_ref = $sth->fetchall_arrayref([0]);
4486 To fetch the second to last and last column of every row:
4488 $tbl_ary_ref = $sth->fetchall_arrayref([-2,-1]);
4490 Those two examples both return a reference to an array of array refs.
4492 If $slice is a hash reference, "fetchall_arrayref" fetches each row as
4494 a hash reference. If the $slice hash is empty then the keys in the
4495 hashes have whatever name lettercase is returned by default. (See
4496 "FetchHashKeyName" attribute.) If the $slice hash is not empty, then it
4497 is used as a slice to select individual columns by name. The values of
4498 the hash should be set to 1. The key names of the returned hashes
4499 match the letter case of the names in the parameter hash, regardless of
4500 the "FetchHashKeyName" attribute.
4501 For example, to fetch all fields of every row as a hash ref:
4503 $tbl_ary_ref = $sth->fetchall_arrayref({});
4505 To fetch only the fields called "foo" and "bar" of every row as a hash
4507 ref (with keys named "foo" and "BAR", regardless of the original
4508 capitalization):
4509 $tbl_ary_ref = $sth->fetchall_arrayref({ foo=>1, BAR=>1 });
4511 Those two examples both return a reference to an array of hash refs.
4513 If $slice is a reference to a hash reference, that hash is used to
4515 select and rename columns. The keys are 0-based column index numbers
4516 and the values are the corresponding keys for the returned row hashes.
4517 For example, to fetch only the first and second columns of every row as
4519 a hash ref (with keys named "k" and "v" regardless of their original
4520 names):
4521 $tbl_ary_ref = $sth->fetchall_arrayref( \{ 0 => 'k', 1 => 'v' } );
4523 If $max_rows is defined and greater than or equal to zero then it is
4525 used to limit the number of rows fetched before returning.
4526 fetchall_arrayref() can then be called again to fetch more rows. This
4527 is especially useful when you need the better performance of
4528 fetchall_arrayref() but don't have enough memory to fetch and return
4529 all the rows in one go.
4530 Here's an example (assumes RaiseError is enabled):
4532 my $rows = []; # cache for batches of rows
4534 while( my $row = ( shift(@$rows) || # get row from cache, or reload cache:
4535 shift(@{$rows=$sth->fetchall_arrayref(undef,10_000)||[]}) )
4536 ) {
4537 ...
4538 }
4539 That might be the fastest way to fetch and process lots of rows using
4541 the DBI, but it depends on the relative cost of method calls vs memory
4542 allocation.
4543 A standard "while" loop with column binding is often faster because the
4545 cost of allocating memory for the batch of rows is greater than the
4546 saving by reducing method calls. It's possible that the DBI may provide
4547 a way to reuse the memory of a previous batch in future, which would
4548 then shift the balance back towards fetchall_arrayref().
4549 "fetchall_hashref"
4551 $hash_ref = $sth->fetchall_hashref($key_field);
4553 The "fetchall_hashref" method can be used to fetch all the data to be
4555 returned from a prepared and executed statement handle. It returns a
4556 reference to a hash containing a key for each distinct value of the
4557 $key_field column that was fetched. For each key the corresponding
4558 value is a reference to a hash containing all the selected columns and
4559 their values, as returned by "fetchrow_hashref()".
4560 If there are no rows to return, "fetchall_hashref" returns a reference
4562 to an empty hash. If an error occurs, "fetchall_hashref" returns the
4563 data fetched thus far, which may be none. You should check "$sth->err"
4564 afterwards (or use the "RaiseError" attribute) to discover if the data
4565 is complete or was truncated due to an error.
4566 The $key_field parameter provides the name of the field that holds the
4568 value to be used for the key for the returned hash. For example:
4569 $dbh->{FetchHashKeyName} = 'NAME_lc';
4571 $sth = $dbh->prepare("SELECT FOO, BAR, ID, NAME, BAZ FROM TABLE");
4572 $sth->execute;
4573 $hash_ref = $sth->fetchall_hashref('id');
4574 print "Name for id 42 is $hash_ref->{42}->{name}\n";
4575 The $key_field parameter can also be specified as an integer column
4577 number (counting from 1). If $key_field doesn't match any column in
4578 the statement, as a name first then as a number, then an error is
4579 returned.
4580 For queries returning more than one 'key' column, you can specify
4582 multiple column names by passing $key_field as a reference to an array
4583 containing one or more key column names (or index numbers). For
4584 example:
4585 $sth = $dbh->prepare("SELECT foo, bar, baz FROM table");
4587 $sth->execute;
4588 $hash_ref = $sth->fetchall_hashref( [ qw(foo bar) ] );
4589 print "For foo 42 and bar 38, baz is $hash_ref->{42}->{38}->{baz}\n";
4590 The fetchall_hashref() method is normally used only where the key
4592 fields values for each row are unique. If multiple rows are returned
4593 with the same values for the key fields then later rows overwrite
4594 earlier ones.
4595 "finish"
4597 $rc = $sth->finish;
4599 Indicate that no more data will be fetched from this statement handle
4601 before it is either executed again or destroyed. You almost certainly
4602 do not need to call this method.
4603 Adding calls to "finish" after loop that fetches all rows is a common
4605 mistake, don't do it, it can mask genuine problems like uncaught fetch
4606 errors.
4607 When all the data has been fetched from a "SELECT" statement, the
4609 driver will automatically call "finish" for you. So you should not call
4610 it explicitly except when you know that you've not fetched all the data
4611 from a statement handle and the handle won't be destroyed soon.
4612 The most common example is when you only want to fetch just one row,
4614 but in that case the "selectrow_*" methods are usually better anyway.
4615 Consider a query like:
4617 SELECT foo FROM table WHERE bar=? ORDER BY baz
4619 on a very large table. When executed, the database server will have to
4621 use temporary buffer space to store the sorted rows. If, after
4622 executing the handle and selecting just a few rows, the handle won't be
4623 re-executed for some time and won't be destroyed, the "finish" method
4624 can be used to tell the server that the buffer space can be freed.
4625 Calling "finish" resets the "Active" attribute for the statement. It
4627 may also make some statement handle attributes (such as "NAME" and
4628 "TYPE") unavailable if they have not already been accessed (and thus
4629 cached).
4630 The "finish" method does not affect the transaction status of the
4632 database connection. It has nothing to do with transactions. It's
4633 mostly an internal "housekeeping" method that is rarely needed. See
4634 also "disconnect" and the "Active" attribute.
4635 The "finish" method should have been called "discard_pending_rows".
4637 "rows"
4639 $rv = $sth->rows;
4641 Returns the number of rows affected by the last row affecting command,
4643 or -1 if the number of rows is not known or not available.
4644 Generally, you can only rely on a row count after a non-"SELECT"
4646 "execute" (for some specific operations like "UPDATE" and "DELETE"), or
4647 after fetching all the rows of a "SELECT" statement.
4648 For "SELECT" statements, it is generally not possible to know how many
4650 rows will be returned except by fetching them all. Some drivers will
4651 return the number of rows the application has fetched so far, but
4652 others may return -1 until all rows have been fetched. So use of the
4653 "rows" method or $DBI::rows with "SELECT" statements is not
4654 recommended.
4655 One alternative method to get a row count for a "SELECT" is to execute
4657 a "SELECT COUNT(*) FROM ..." SQL statement with the same "..." as your
4658 query and then fetch the row count from that.
4659 "bind_col"
4661 $rc = $sth->bind_col($column_number, \$var_to_bind);
4663 $rc = $sth->bind_col($column_number, \$var_to_bind, \%attr );
4664 $rc = $sth->bind_col($column_number, \$var_to_bind, $bind_type );
4665 Binds a Perl variable and/or some attributes to an output column
4667 (field) of a "SELECT" statement. Column numbers count up from 1. You
4668 do not need to bind output columns in order to fetch data. For maximum
4669 portability between drivers, bind_col() should be called after
4670 execute() and not before. See also "bind_columns" for an example.
4671 The binding is performed at a low level using Perl aliasing. Whenever
4673 a row is fetched from the database $var_to_bind appears to be
4674 automatically updated simply because it now refers to the same memory
4675 location as the corresponding column value. This makes using bound
4676 variables very efficient. Binding a tied variable doesn't work,
4677 currently.
4678 The "bind_param" method performs a similar, but opposite, function for
4680 input variables.
4681 Data Types for Column Binding
4683 The "\%attr" parameter can be used to hint at the data type formatting
4685 the column should have. For example, you can use:
4686 $sth->bind_col(1, undef, { TYPE => SQL_DATETIME });
4688 to specify that you'd like the column (which presumably is some kind of
4690 datetime type) to be returned in the standard format for SQL_DATETIME,
4691 which is 'YYYY-MM-DD HH:MM:SS', rather than the native formatting the
4692 database would normally use.
4693 There's no $var_to_bind in that example to emphasize the point that
4695 bind_col() works on the underlying column and not just a particular
4696 bound variable.
4697 As a short-cut for the common case, the data type can be passed
4699 directly, in place of the "\%attr" hash reference. This example is
4700 equivalent to the one above:
4701 $sth->bind_col(1, undef, SQL_DATETIME);
4703 The "TYPE" value indicates the standard (non-driver-specific) type for
4705 this parameter. To specify the driver-specific type, the driver may
4706 support a driver-specific attribute, such as "{ ora_type => 97 }".
4707 The SQL_DATETIME and other related constants can be imported using
4709 use DBI qw(:sql_types);
4711 See "DBI Constants" for more information.
4713 Few drivers support specifying a data type via a "bind_col" call (most
4715 will simply ignore the data type). Fewer still allow the data type to
4716 be altered once set. If you do set a column type the type should remain
4717 sticky through further calls to bind_col for the same column if the
4718 type is not overridden (this is important for instance when you are
4719 using a slice in fetchall_arrayref).
4720 The TYPE attribute for bind_col() was first specified in DBI 1.41.
4722 From DBI 1.611, drivers can use the "TYPE" attribute to attempt to cast
4724 the bound scalar to a perl type which more closely matches "TYPE". At
4725 present DBI supports "SQL_INTEGER", "SQL_DOUBLE" and "SQL_NUMERIC". See
4726 "sql_type_cast" for details of how types are cast.
4727 Other attributes for Column Binding
4729 The "\%attr" parameter may also contain the following attributes:
4731 "StrictlyTyped"
4733 If a "TYPE" attribute is passed to bind_col, then the driver will
4734 attempt to change the bound perl scalar to match the type more
4735 closely. If the bound value cannot be cast to the requested "TYPE"
4736 then by default it is left untouched and no error is generated. If
4737 you specify "StrictlyTyped" as 1 and the cast fails, this will
4738 generate an error.
4739 This attribute was first added in DBI 1.611. When 1.611 was
4741 released few drivers actually supported this attribute but
4742 DBD::Oracle and DBD::ODBC should from versions 1.24.
4743 "DiscardString"
4745 When the "TYPE" attribute is passed to "bind_col" and the driver
4746 successfully casts the bound perl scalar to a non-string type then
4747 if "DiscardString" is set to 1, the string portion of the scalar
4748 will be discarded. By default, "DiscardString" is not set.
4749 This attribute was first added in DBI 1.611. When 1.611 was
4751 released few drivers actually supported this attribute but
4752 DBD::Oracle and DBD::ODBC should from versions 1.24.
4753 "bind_columns"
4755 $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
4757 Calls "bind_col" for each column of the "SELECT" statement.
4759 The list of references should have the same number of elements as the
4761 number of columns in the "SELECT" statement. If it doesn't then
4762 "bind_columns" will bind the elements given, up to the number of
4763 columns, and then return an error.
4764 For maximum portability between drivers, bind_columns() should be
4766 called after execute() and not before.
4767 For example:
4769 $dbh->{RaiseError} = 1; # do this, or check every call for errors
4771 $sth = $dbh->prepare(q{ SELECT region, sales FROM sales_by_region });
4772 $sth->execute;
4773 my ($region, $sales);
4774 # Bind Perl variables to columns:
4776 $rv = $sth->bind_columns(\$region, \$sales);
4777 # you can also use Perl's \(...) syntax (see perlref docs):
4779 # $sth->bind_columns(\($region, $sales));
4780 # Column binding is the most efficient way to fetch data
4782 while ($sth->fetch) {
4783 print "$region: $sales\n";
4784 }
4785 For compatibility with old scripts, the first parameter will be ignored
4787 if it is "undef" or a hash reference.
4788 Here's a more fancy example that binds columns to the values inside a
4790 hash (thanks to H.Merijn Brand):
4791 $sth->execute;
4793 my %row;
4794 $sth->bind_columns( \( @row{ @{$sth->{NAME_lc} } } ));
4795 while ($sth->fetch) {
4796 print "$row{region}: $row{sales}\n";
4797 }
4798 "dump_results"
4800 $rows = $sth->dump_results($maxlen, $lsep, $fsep, $fh);
4802 Fetches all the rows from $sth, calls "DBI::neat_list" for each row,
4804 and prints the results to $fh (defaults to "STDOUT") separated by $lsep
4805 (default "\n"). $fsep defaults to ", " and $maxlen defaults to 35.
4806 This method is designed as a handy utility for prototyping and testing
4808 queries. Since it uses "neat_list" to format and edit the string for
4809 reading by humans, it is not recommended for data transfer
4810 applications.
4811 Statement Handle Attributes
4813 This section describes attributes specific to statement handles. Most
4814 of these attributes are read-only.
4815 Changes to these statement handle attributes do not affect any other
4817 existing or future statement handles.
4818 Attempting to set or get the value of an unknown attribute generates a
4820 warning, except for private driver specific attributes (which all have
4821 names starting with a lowercase letter).
4822 Example:
4824 ... = $h->{NUM_OF_FIELDS}; # get/read
4826 Some drivers cannot provide valid values for some or all of these
4828 attributes until after "$sth->execute" has been successfully called.
4829 Typically the attribute will be "undef" in these situations.
4830 Some attributes, like NAME, are not appropriate to some types of
4832 statement, like SELECT. Typically the attribute will be "undef" in
4833 these situations.
4834 For drivers which support stored procedures and multiple result sets
4836 (see "more_results") these attributes relate to the current result set.
4837 See also "finish" to learn more about the effect it may have on some
4839 attributes.
4840 "NUM_OF_FIELDS"
4842 Type: integer, read-only
4844 Number of fields (columns) in the data the prepared statement may
4846 return. Statements that don't return rows of data, like "DELETE" and
4847 "CREATE" set "NUM_OF_FIELDS" to 0 (though it may be undef in some
4848 drivers).
4849 "NUM_OF_PARAMS"
4851 Type: integer, read-only
4853 The number of parameters (placeholders) in the prepared statement. See
4855 SUBSTITUTION VARIABLES below for more details.
4856 "NAME"
4858 Type: array-ref, read-only
4860 Returns a reference to an array of field names for each column. The
4862 names may contain spaces but should not be truncated or have any
4863 trailing space. Note that the names have the letter case (upper, lower
4864 or mixed) as returned by the driver being used. Portable applications
4865 should use "NAME_lc" or "NAME_uc".
4866 print "First column name: $sth->{NAME}->[0]\n";
4868 Also note that the name returned for (aggregate) functions like
4870 count(*) or "max(c_foo)" is determined by the database server and not
4871 by "DBI" or the "DBD" backend.
4872 "NAME_lc"
4874 Type: array-ref, read-only
4876 Like "/NAME" but always returns lowercase names.
4878 "NAME_uc"
4880 Type: array-ref, read-only
4882 Like "/NAME" but always returns uppercase names.
4884 "NAME_hash"
4886 Type: hash-ref, read-only
4888 "NAME_lc_hash"
4890 Type: hash-ref, read-only
4892 "NAME_uc_hash"
4894 Type: hash-ref, read-only
4896 The "NAME_hash", "NAME_lc_hash", and "NAME_uc_hash" attributes return
4898 column name information as a reference to a hash.
4899 The keys of the hash are the names of the columns. The letter case of
4901 the keys corresponds to the letter case returned by the "NAME",
4902 "NAME_lc", and "NAME_uc" attributes respectively (as described above).
4903 The value of each hash entry is the perl index number of the
4905 corresponding column (counting from 0). For example:
4906 $sth = $dbh->prepare("select Id, Name from table");
4908 $sth->execute;
4909 @row = $sth->fetchrow_array;
4910 print "Name $row[ $sth->{NAME_lc_hash}{name} ]\n";
4911 "TYPE"
4913 Type: array-ref, read-only
4915 Returns a reference to an array of integer values for each column. The
4917 value indicates the data type of the corresponding column.
4918 The values correspond to the international standards (ANSI X3.135 and
4920 ISO/IEC 9075) which, in general terms, means ODBC. Driver-specific
4921 types that don't exactly match standard types should generally return
4922 the same values as an ODBC driver supplied by the makers of the
4923 database. That might include private type numbers in ranges the vendor
4924 has officially registered with the ISO working group:
4925 ftp://sqlstandards.org/SC32/SQL_Registry/
4927 Where there's no vendor-supplied ODBC driver to be compatible with, the
4929 DBI driver can use type numbers in the range that is now officially
4930 reserved for use by the DBI: -9999 to -9000.
4931 All possible values for "TYPE" should have at least one entry in the
4933 output of the "type_info_all" method (see "type_info_all").
4934 "PRECISION"
4936 Type: array-ref, read-only
4938 Returns a reference to an array of integer values for each column.
4940 For numeric columns, the value is the maximum number of digits (without
4942 considering a sign character or decimal point). Note that the "display
4943 size" for floating point types (REAL, FLOAT, DOUBLE) can be up to 7
4944 characters greater than the precision (for the sign + decimal point +
4945 the letter E + a sign + 2 or 3 digits).
4946 For any character type column the value is the OCTET_LENGTH, in other
4948 words the number of bytes, not characters.
4949 (More recent standards refer to this as COLUMN_SIZE but we stick with
4951 PRECISION for backwards compatibility.)
4952 "SCALE"
4954 Type: array-ref, read-only
4956 Returns a reference to an array of integer values for each column.
4958 NULL ("undef") values indicate columns where scale is not applicable.
4959 "NULLABLE"
4961 Type: array-ref, read-only
4963 Returns a reference to an array indicating the possibility of each
4965 column returning a null. Possible values are 0 (or an empty string) =
4966 no, 1 = yes, 2 = unknown.
4967 print "First column may return NULL\n" if $sth->{NULLABLE}->[0];
4969 "CursorName"
4971 Type: string, read-only
4973 Returns the name of the cursor associated with the statement handle, if
4975 available. If not available or if the database driver does not support
4976 the "where current of ..." SQL syntax, then it returns "undef".
4977 "Database"
4979 Type: dbh, read-only
4981 Returns the parent $dbh of the statement handle.
4983 "Statement"
4985 Type: string, read-only
4987 Returns the statement string passed to the "prepare" method.
4989 "ParamValues"
4991 Type: hash ref, read-only
4993 Returns a reference to a hash containing the values currently bound to
4995 placeholders. The keys of the hash are the 'names' of the
4996 placeholders, typically integers starting at 1. Returns undef if not
4997 supported by the driver.
4998 See "ShowErrorStatement" for an example of how this is used.
5000 * Keys:
5002 If the driver supports "ParamValues" but no values have been bound yet
5004 then the driver should return a hash with placeholders names in the
5005 keys but all the values undef, but some drivers may return a ref to an
5006 empty hash because they can't pre-determine the names.
5007 It is possible that the keys in the hash returned by "ParamValues" are
5009 not exactly the same as those implied by the prepared statement. For
5010 example, DBD::Oracle translates '"?"' placeholders into '":pN"' where N
5011 is a sequence number starting at 1.
5012 * Values:
5014 It is possible that the values in the hash returned by "ParamValues"
5016 are not exactly the same as those passed to bind_param() or execute().
5017 The driver may have slightly modified values in some way based on the
5018 TYPE the value was bound with. For example a floating point value bound
5019 as an SQL_INTEGER type may be returned as an integer. The values
5020 returned by "ParamValues" can be passed to another bind_param() method
5021 with the same TYPE and will be seen by the database as the same value.
5022 See also "ParamTypes" below.
5023 The "ParamValues" attribute was added in DBI 1.28.
5025 "ParamTypes"
5027 Type: hash ref, read-only
5029 Returns a reference to a hash containing the type information currently
5031 bound to placeholders. Returns undef if not supported by the driver.
5032 * Keys:
5034 See "ParamValues" above.
5036 * Values:
5038 The hash values are hashrefs of type information in the same form as
5040 that passed to the various bind_param() methods (See "bind_param" for
5041 the format and values).
5042 It is possible that the values in the hash returned by "ParamTypes" are
5044 not exactly the same as those passed to bind_param() or execute().
5045 Param attributes specified using the abbreviated form, like this:
5046 $sth->bind_param(1, SQL_INTEGER);
5048 are returned in the expanded form, as if called like this:
5050 $sth->bind_param(1, { TYPE => SQL_INTEGER });
5052 The driver may have modified the type information in some way based on
5054 the bound values, other hints provided by the prepare()'d SQL
5055 statement, or alternate type mappings required by the driver or target
5056 database system. The driver may also add private keys (with names
5057 beginning with the drivers reserved prefix, e.g., odbc_xxx).
5058 * Example:
5060 The keys and values in the returned hash can be passed to the various
5062 bind_param() methods to effectively reproduce a previous param binding.
5063 For example:
5064 # assuming $sth1 is a previously prepared statement handle
5066 my $sth2 = $dbh->prepare( $sth1->{Statement} );
5067 my $ParamValues = $sth1->{ParamValues} || {};
5068 my $ParamTypes = $sth1->{ParamTypes} || {};
5069 $sth2->bind_param($_, $ParamValues->{$_}, $ParamTypes->{$_})
5070 for keys %{ {%$ParamValues, %$ParamTypes} };
5071 $sth2->execute();
5072 The "ParamTypes" attribute was added in DBI 1.49. Implementation is the
5074 responsibility of individual drivers; the DBI layer default
5075 implementation simply returns undef.
5076 "ParamArrays"
5078 Type: hash ref, read-only
5080 Returns a reference to a hash containing the values currently bound to
5082 placeholders with "execute_array" or "bind_param_array". The keys of
5083 the hash are the 'names' of the placeholders, typically integers
5084 starting at 1. Returns undef if not supported by the driver or no
5085 arrays of parameters are bound.
5086 Each key value is an array reference containing a list of the bound
5088 parameters for that column.
5089 For example:
5091 $sth = $dbh->prepare("INSERT INTO staff (id, name) values (?,?)");
5093 $sth->execute_array({},[1,2], ['fred','dave']);
5094 if ($sth->{ParamArrays}) {
5095 foreach $param (keys %{$sth->{ParamArrays}}) {
5096 printf "Parameters for %s : %s\n", $param,
5097 join(",", @{$sth->{ParamArrays}->{$param}});
5098 }
5099 }
5100 It is possible that the values in the hash returned by "ParamArrays"
5102 are not exactly the same as those passed to "bind_param_array" or
5103 "execute_array". The driver may have slightly modified values in some
5104 way based on the TYPE the value was bound with. For example a floating
5105 point value bound as an SQL_INTEGER type may be returned as an integer.
5106 It is also possible that the keys in the hash returned by "ParamArrays"
5108 are not exactly the same as those implied by the prepared statement.
5109 For example, DBD::Oracle translates '"?"' placeholders into '":pN"'
5110 where N is a sequence number starting at 1.
5111 "RowsInCache"
5113 Type: integer, read-only
5115 If the driver supports a local row cache for "SELECT" statements, then
5117 this attribute holds the number of un-fetched rows in the cache. If the
5118 driver doesn't, then it returns "undef". Note that some drivers pre-
5119 fetch rows on execute, whereas others wait till the first fetch.
5120 See also the "RowCacheSize" database handle attribute.
5122
5124 Catalog Methods
5125 An application can retrieve metadata information from the DBMS by
5126 issuing appropriate queries on the views of the Information Schema.
5127 Unfortunately, "INFORMATION_SCHEMA" views are seldom supported by the
5128 DBMS. Special methods (catalog methods) are available to return result
5129 sets for a small but important portion of that metadata:
5130 column_info
5132 foreign_key_info
5133 primary_key_info
5134 table_info
5135 statistics_info
5136 All catalog methods accept arguments in order to restrict the result
5138 sets. Passing "undef" to an optional argument does not constrain the
5139 search for that argument. However, an empty string ('') is treated as
5140 a regular search criteria and will only match an empty value.
5141 Note: SQL/CLI and ODBC differ in the handling of empty strings. An
5143 empty string will not restrict the result set in SQL/CLI.
5144 Most arguments in the catalog methods accept only ordinary values, e.g.
5146 the arguments of "primary_key_info()". Such arguments are treated as a
5147 literal string, i.e. the case is significant and quote characters are
5148 taken literally.
5149 Some arguments in the catalog methods accept search patterns (strings
5151 containing '_' and/or '%'), e.g. the $table argument of
5152 "column_info()". Passing '%' is equivalent to leaving the argument
5153 "undef".
5154 Caveat: The underscore ('_') is valid and often used in SQL
5156 identifiers. Passing such a value to a search pattern argument may
5157 return more rows than expected! To include pattern characters as
5158 literals, they must be preceded by an escape character which can be
5159 achieved with
5160 $esc = $dbh->get_info( 14 ); # SQL_SEARCH_PATTERN_ESCAPE
5162 $search_pattern =~ s/([_%])/$esc$1/g;
5163 The ODBC and SQL/CLI specifications define a way to change the default
5165 behaviour described above: All arguments (except list value arguments)
5166 are treated as identifier if the "SQL_ATTR_METADATA_ID" attribute is
5167 set to "SQL_TRUE". Quoted identifiers are very similar to ordinary
5168 values, i.e. their body (the string within the quotes) is interpreted
5169 literally. Unquoted identifiers are compared in UPPERCASE.
5170 The DBI (currently) does not support the "SQL_ATTR_METADATA_ID"
5172 attribute, i.e. it behaves like an ODBC driver where
5173 "SQL_ATTR_METADATA_ID" is set to "SQL_FALSE".
5174 Transactions
5176 Transactions are a fundamental part of any robust database system. They
5177 protect against errors and database corruption by ensuring that sets of
5178 related changes to the database take place in atomic (indivisible, all-
5179 or-nothing) units.
5180 This section applies to databases that support transactions and where
5182 "AutoCommit" is off. See "AutoCommit" for details of using
5183 "AutoCommit" with various types of databases.
5184 The recommended way to implement robust transactions in Perl
5186 applications is to enable "RaiseError" and catch the error that's
5187 'thrown' as an exception. For example, using Try::Tiny:
5188 use Try::Tiny;
5190 $dbh->{AutoCommit} = 0; # enable transactions, if possible
5191 $dbh->{RaiseError} = 1;
5192 try {
5193 foo(...) # do lots of work here
5194 bar(...) # including inserts
5195 baz(...) # and updates
5196 $dbh->commit; # commit the changes if we get this far
5197 } catch {
5198 warn "Transaction aborted because $_"; # Try::Tiny copies $@ into $_
5199 # now rollback to undo the incomplete changes
5200 # but do it in an eval{} as it may also fail
5201 eval { $dbh->rollback };
5202 # add other application on-error-clean-up code here
5203 };
5204 If the "RaiseError" attribute is not set, then DBI calls would need to
5206 be manually checked for errors, typically like this:
5207 $h->method(@args) or die $h->errstr;
5209 With "RaiseError" set, the DBI will automatically "die" if any DBI
5211 method call on that handle (or a child handle) fails, so you don't have
5212 to test the return value of each method call. See "RaiseError" for more
5213 details.
5214 A major advantage of the "eval" approach is that the transaction will
5216 be properly rolled back if any code (not just DBI calls) in the inner
5217 application dies for any reason. The major advantage of using the
5218 "$h->{RaiseError}" attribute is that all DBI calls will be checked
5219 automatically. Both techniques are strongly recommended.
5220 After calling "commit" or "rollback" many drivers will not let you
5222 fetch from a previously active "SELECT" statement handle that's a child
5223 of the same database handle. A typical way round this is to connect the
5224 the database twice and use one connection for "SELECT" statements.
5225 See "AutoCommit" and "disconnect" for other important information about
5227 transactions.
5228 Handling BLOB / LONG / Memo Fields
5230 Many databases support "blob" (binary large objects), "long", or
5231 similar datatypes for holding very long strings or large amounts of
5232 binary data in a single field. Some databases support variable length
5233 long values over 2,000,000,000 bytes in length.
5234 Since values of that size can't usually be held in memory, and because
5236 databases can't usually know in advance the length of the longest long
5237 that will be returned from a "SELECT" statement (unlike other data
5238 types), some special handling is required.
5239 In this situation, the value of the "$h->{LongReadLen}" attribute is
5241 used to determine how much buffer space to allocate when fetching such
5242 fields. The "$h->{LongTruncOk}" attribute is used to determine how to
5243 behave if a fetched value can't fit into the buffer.
5244 See the description of "LongReadLen" for more information.
5246 When trying to insert long or binary values, placeholders should be
5248 used since there are often limits on the maximum size of an "INSERT"
5249 statement and the "quote" method generally can't cope with binary data.
5250 See "Placeholders and Bind Values".
5251 Simple Examples
5253 Here's a complete example program to select and fetch some data:
5254 my $data_source = "dbi::DriverName:db_name";
5256 my $dbh = DBI->connect($data_source, $user, $password)
5257 or die "Can't connect to $data_source: $DBI::errstr";
5258 my $sth = $dbh->prepare( q{
5260 SELECT name, phone
5261 FROM mytelbook
5262 }) or die "Can't prepare statement: $DBI::errstr";
5263 my $rc = $sth->execute
5265 or die "Can't execute statement: $DBI::errstr";
5266 print "Query will return $sth->{NUM_OF_FIELDS} fields.\n\n";
5268 print "Field names: @{ $sth->{NAME} }\n";
5269 while (($name, $phone) = $sth->fetchrow_array) {
5271 print "$name: $phone\n";
5272 }
5273 # check for problems which may have terminated the fetch early
5274 die $sth->errstr if $sth->err;
5275 $dbh->disconnect;
5277 Here's a complete example program to insert some data from a file.
5279 (This example uses "RaiseError" to avoid needing to check each call).
5280 my $dbh = DBI->connect("dbi:DriverName:db_name", $user, $password, {
5282 RaiseError => 1, AutoCommit => 0
5283 });
5284 my $sth = $dbh->prepare( q{
5286 INSERT INTO table (name, phone) VALUES (?, ?)
5287 });
5288 open FH, "<phone.csv" or die "Unable to open phone.csv: $!";
5290 while (<FH>) {
5291 chomp;
5292 my ($name, $phone) = split /,/;
5293 $sth->execute($name, $phone);
5294 }
5295 close FH;
5296 $dbh->commit;
5298 $dbh->disconnect;
5299 Here's how to convert fetched NULLs (undefined values) into empty
5301 strings:
5302 while($row = $sth->fetchrow_arrayref) {
5304 # this is a fast and simple way to deal with nulls:
5305 foreach (@$row) { $_ = '' unless defined }
5306 print "@$row\n";
5307 }
5308 The "q{...}" style quoting used in these examples avoids clashing with
5310 quotes that may be used in the SQL statement. Use the double-quote like
5311 "qq{...}" operator if you want to interpolate variables into the
5312 string. See "Quote and Quote-like Operators" in perlop for more
5313 details.
5314 Threads and Thread Safety
5316 Perl 5.7 and later support a new threading model called iThreads. (The
5317 old "5.005 style" threads are not supported by the DBI.)
5318 In the iThreads model each thread has its own copy of the perl
5320 interpreter. When a new thread is created the original perl
5321 interpreter is 'cloned' to create a new copy for the new thread.
5322 If the DBI and drivers are loaded and handles created before the thread
5324 is created then it will get a cloned copy of the DBI, the drivers and
5325 the handles.
5326 However, the internal pointer data within the handles will refer to the
5328 DBI and drivers in the original interpreter. Using those handles in the
5329 new interpreter thread is not safe, so the DBI detects this and croaks
5330 on any method call using handles that don't belong to the current
5331 thread (except for DESTROY).
5332 Because of this (possibly temporary) restriction, newly created threads
5334 must make their own connections to the database. Handles can't be
5335 shared across threads.
5336 But BEWARE, some underlying database APIs (the code the DBD driver uses
5338 to talk to the database, often supplied by the database vendor) are not
5339 thread safe. If it's not thread safe, then allowing more than one
5340 thread to enter the code at the same time may cause subtle/serious
5341 problems. In some cases allowing more than one thread to enter the
5342 code, even if not at the same time, can cause problems. You have been
5343 warned.
5344 Using DBI with perl threads is not yet recommended for production
5346 environments. For more information see
5347 <http://www.perlmonks.org/index.pl?node_id=288022>
5348 Note: There is a bug in perl 5.8.2 when configured with threads and
5350 debugging enabled (bug #24463) which causes a DBI test to fail.
5351 Signal Handling and Canceling Operations
5353 [The following only applies to systems with unix-like signal handling.
5354 I'd welcome additions for other systems, especially Windows.]
5355 The first thing to say is that signal handling in Perl versions less
5357 than 5.8 is not safe. There is always a small risk of Perl crashing
5358 and/or core dumping when, or after, handling a signal because the
5359 signal could arrive and be handled while internal data structures are
5360 being changed. If the signal handling code used those same internal
5361 data structures it could cause all manner of subtle and not-so-subtle
5362 problems. The risk was reduced with 5.4.4 but was still present in all
5363 perls up through 5.8.0.
5364 Beginning in perl 5.8.0 perl implements 'safe' signal handling if your
5366 system has the POSIX sigaction() routine. Now when a signal is
5367 delivered perl just makes a note of it but does not run the %SIG
5368 handler. The handling is 'deferred' until a 'safe' moment.
5369 Although this change made signal handling safe, it also lead to a
5371 problem with signals being deferred for longer than you'd like. If a
5372 signal arrived while executing a system call, such as waiting for data
5373 on a network connection, the signal is noted and then the system call
5374 that was executing returns with an EINTR error code to indicate that it
5375 was interrupted. All fine so far.
5376 The problem comes when the code that made the system call sees the
5378 EINTR code and decides it's going to call it again. Perl doesn't do
5379 that, but database code sometimes does. If that happens then the signal
5380 handler doesn't get called until later. Maybe much later.
5381 Fortunately there are ways around this which we'll discuss below.
5383 Unfortunately they make signals unsafe again.
5384 The two most common uses of signals in relation to the DBI are for
5386 canceling operations when the user types Ctrl-C (interrupt), and for
5387 implementing a timeout using "alarm()" and $SIG{ALRM}.
5388 Cancel
5390 The DBI provides a "cancel" method for statement handles. The
5391 "cancel" method should abort the current operation and is designed
5392 to be called from a signal handler. For example:
5393 $SIG{INT} = sub { $sth->cancel };
5395 However, few drivers implement this (the DBI provides a default
5397 method that just returns "undef") and, even if implemented, there
5398 is still a possibility that the statement handle, and even the
5399 parent database handle, will not be usable afterwards.
5400 If "cancel" returns true, then it has successfully invoked the
5402 database engine's own cancel function. If it returns false, then
5403 "cancel" failed. If it returns "undef", then the database driver
5404 does not have cancel implemented - very few do.
5405 Timeout
5407 The traditional way to implement a timeout is to set $SIG{ALRM} to
5408 refer to some code that will be executed when an ALRM signal
5409 arrives and then to call alarm($seconds) to schedule an ALRM signal
5410 to be delivered $seconds in the future. For example:
5411 my $failed;
5413 eval {
5414 local $SIG{ALRM} = sub { die "TIMEOUT\n" }; # N.B. \n required
5415 eval {
5416 alarm($seconds);
5417 ... code to execute with timeout here (which may die) ...
5418 1;
5419 } or $failed = 1;
5420 # outer eval catches alarm that might fire JUST before this alarm(0)
5421 alarm(0); # cancel alarm (if code ran fast)
5422 die "$@" if $failed;
5423 1;
5424 } or $failed = 1;
5425 if ( $failed ) {
5426 if ( defined $@ and $@ eq "TIMEOUT\n" ) { ... }
5427 else { ... } # some other error
5428 }
5429 The first (outer) eval is used to avoid the unlikely but possible
5431 chance that the "code to execute" dies and the alarm fires before
5432 it is cancelled. Without the outer eval, if this happened your
5433 program will die if you have no ALRM handler or a non-local alarm
5434 handler will be called.
5435 Unfortunately, as described above, this won't always work as
5437 expected, depending on your perl version and the underlying
5438 database code.
5439 With Oracle for instance (DBD::Oracle), if the system which hosts
5441 the database is down the DBI->connect() call will hang for several
5442 minutes before returning an error.
5443 The solution on these systems is to use the "POSIX::sigaction()"
5445 routine to gain low level access to how the signal handler is
5446 installed.
5447 The code would look something like this (for the DBD-Oracle connect()):
5449 use POSIX qw(:signal_h);
5451 my $mask = POSIX::SigSet->new( SIGALRM ); # signals to mask in the handler
5453 my $action = POSIX::SigAction->new(
5454 sub { die "connect timeout\n" }, # the handler code ref
5455 $mask,
5456 # not using (perl 5.8.2 and later) 'safe' switch or sa_flags
5457 );
5458 my $oldaction = POSIX::SigAction->new();
5459 sigaction( SIGALRM, $action, $oldaction );
5460 my $dbh;
5461 my $failed;
5462 eval {
5463 eval {
5464 alarm(5); # seconds before time out
5465 $dbh = DBI->connect("dbi:Oracle:$dsn" ... );
5466 1;
5467 } or $failed = 1;
5468 alarm(0); # cancel alarm (if connect worked fast)
5469 die "$@\n" if $failed; # connect died
5470 1;
5471 } or $failed = 1;
5472 sigaction( SIGALRM, $oldaction ); # restore original signal handler
5473 if ( $failed ) {
5474 if ( defined $@ and $@ eq "connect timeout\n" ) {...}
5475 else { # connect died }
5476 }
5477 See previous example for the reasoning around the double eval.
5479 Similar techniques can be used for canceling statement execution.
5481 Unfortunately, this solution is somewhat messy, and it does not work
5483 with perl versions less than perl 5.8 where "POSIX::sigaction()"
5484 appears to be broken.
5485 For a cleaner implementation that works across perl versions, see
5487 Lincoln Baxter's Sys::SigAction module at Sys::SigAction. The
5488 documentation for Sys::SigAction includes an longer discussion of this
5489 problem, and a DBD::Oracle test script.
5490 Be sure to read all the signal handling sections of the perlipc manual.
5492 And finally, two more points to keep firmly in mind. Firstly, remember
5494 that what we've done here is essentially revert to old style unsafe
5495 handling of these signals. So do as little as possible in the handler.
5496 Ideally just die(). Secondly, the handles in use at the time the signal
5497 is handled may not be safe to use afterwards.
5498 Subclassing the DBI
5500 DBI can be subclassed and extended just like any other object oriented
5501 module. Before we talk about how to do that, it's important to be
5502 clear about the various DBI classes and how they work together.
5503 By default "$dbh = DBI->connect(...)" returns a $dbh blessed into the
5505 "DBI::db" class. And the "$dbh->prepare" method returns an $sth
5506 blessed into the "DBI::st" class (actually it simply changes the last
5507 four characters of the calling handle class to be "::st").
5508 The leading '"DBI"' is known as the 'root class' and the extra '"::db"'
5510 or '"::st"' are the 'handle type suffixes'. If you want to subclass the
5511 DBI you'll need to put your overriding methods into the appropriate
5512 classes. For example, if you want to use a root class of "MySubDBI"
5513 and override the do(), prepare() and execute() methods, then your do()
5514 and prepare() methods should be in the "MySubDBI::db" class and the
5515 execute() method should be in the "MySubDBI::st" class.
5516 To setup the inheritance hierarchy the @ISA variable in "MySubDBI::db"
5518 should include "DBI::db" and the @ISA variable in "MySubDBI::st" should
5519 include "DBI::st". The "MySubDBI" root class itself isn't currently
5520 used for anything visible and so, apart from setting @ISA to include
5521 "DBI", it can be left empty.
5522 So, having put your overriding methods into the right classes, and
5524 setup the inheritance hierarchy, how do you get the DBI to use them?
5525 You have two choices, either a static method call using the name of
5526 your subclass:
5527 $dbh = MySubDBI->connect(...);
5529 or specifying a "RootClass" attribute:
5531 $dbh = DBI->connect(..., { RootClass => 'MySubDBI' });
5533 If both forms are used then the attribute takes precedence.
5535 The only differences between the two are that using an explicit
5537 RootClass attribute will a) make the DBI automatically attempt to load
5538 a module by that name if the class doesn't exist, and b) won't call
5539 your MySubDBI::connect() method, if you have one.
5540 When subclassing is being used then, after a successful new connect,
5542 the DBI->connect method automatically calls:
5543 $dbh->connected($dsn, $user, $pass, \%attr);
5545 The default method does nothing. The call is made just to simplify any
5547 post-connection setup that your subclass may want to perform. The
5548 parameters are the same as passed to DBI->connect. If your subclass
5549 supplies a connected method, it should be part of the MySubDBI::db
5550 package.
5551 One more thing to note: you must let the DBI do the handle creation.
5553 If you want to override the connect() method in your *::dr class then
5554 it must still call SUPER::connect to get a $dbh to work with.
5555 Similarly, an overridden prepare() method in *::db must still call
5556 SUPER::prepare to get a $sth. If you try to create your own handles
5557 using bless() then you'll find the DBI will reject them with an "is not
5558 a DBI handle (has no magic)" error.
5559 Here's a brief example of a DBI subclass. A more thorough example can
5561 be found in t/subclass.t in the DBI distribution.
5562 package MySubDBI;
5564 use strict;
5566 use DBI;
5568 use vars qw(@ISA);
5569 @ISA = qw(DBI);
5570 package MySubDBI::db;
5572 use vars qw(@ISA);
5573 @ISA = qw(DBI::db);
5574 sub prepare {
5576 my ($dbh, @args) = @_;
5577 my $sth = $dbh->SUPER::prepare(@args)
5578 or return;
5579 $sth->{private_mysubdbi_info} = { foo => 'bar' };
5580 return $sth;
5581 }
5582 package MySubDBI::st;
5584 use vars qw(@ISA);
5585 @ISA = qw(DBI::st);
5586 sub fetch {
5588 my ($sth, @args) = @_;
5589 my $row = $sth->SUPER::fetch(@args)
5590 or return;
5591 do_something_magical_with_row_data($row)
5592 or return $sth->set_err(1234, "The magic failed", undef, "fetch");
5593 return $row;
5594 }
5595 When calling a SUPER::method that returns a handle, be careful to check
5597 the return value before trying to do other things with it in your
5598 overridden method. This is especially important if you want to set a
5599 hash attribute on the handle, as Perl's autovivification will bite you
5600 by (in)conveniently creating an unblessed hashref, which your method
5601 will then return with usually baffling results later on like the error
5602 "dbih_getcom handle HASH(0xa4451a8) is not a DBI handle (has no magic".
5603 It's best to check right after the call and return undef immediately on
5604 error, just like DBI would and just like the example above.
5605 If your method needs to record an error it should call the set_err()
5607 method with the error code and error string, as shown in the example
5608 above. The error code and error string will be recorded in the handle
5609 and available via "$h->err" and $DBI::errstr etc. The set_err() method
5610 always returns an undef or empty list as appropriate. Since your method
5611 should nearly always return an undef or empty list as soon as an error
5612 is detected it's handy to simply return what set_err() returns, as
5613 shown in the example above.
5614 If the handle has "RaiseError", "PrintError", or "HandleError" etc. set
5616 then the set_err() method will honour them. This means that if
5617 "RaiseError" is set then set_err() won't return in the normal way but
5618 will 'throw an exception' that can be caught with an "eval" block.
5619 You can stash private data into DBI handles via "$h->{private_..._*}".
5621 See the entry under "ATTRIBUTES COMMON TO ALL HANDLES" for info and
5622 important caveats.
5623 Memory Leaks
5625 When tracking down memory leaks using tools like Devel::Leak you'll
5626 find that some DBI internals are reported as 'leaking' memory. This is
5627 very unlikely to be a real leak. The DBI has various caches to improve
5628 performance and the apparrent leaks are simply the normal operation of
5629 these caches.
5630 The most frequent sources of the apparrent leaks are "ChildHandles",
5632 "prepare_cached" and "connect_cached".
5633 For example
5635 http://stackoverflow.com/questions/13338308/perl-dbi-memory-leak
5636 Given how widely the DBI is used, you can rest assured that if a new
5638 release of the DBI did have a real leak it would be discovered,
5639 reported, and fixed immediately. The leak you're looking for is
5640 probably elsewhere. Good luck!
5641
5643 The DBI has a powerful tracing mechanism built in. It enables you to
5644 see what's going on 'behind the scenes', both within the DBI and the
5645 drivers you're using.
5646 Trace Settings
5648 Which details are written to the trace output is controlled by a
5649 combination of a trace level, an integer from 0 to 15, and a set of
5650 trace flags that are either on or off. Together these are known as the
5651 trace settings and are stored together in a single integer. For normal
5652 use you only need to set the trace level, and generally only to a value
5653 between 1 and 4.
5654 Each handle has its own trace settings, and so does the DBI. When you
5656 call a method the DBI merges the handles settings into its own for the
5657 duration of the call: the trace flags of the handle are OR'd into the
5658 trace flags of the DBI, and if the handle has a higher trace level then
5659 the DBI trace level is raised to match it. The previous DBI trace
5660 settings are restored when the called method returns.
5661 Trace Levels
5663 Trace levels are as follows:
5664 0 - Trace disabled.
5666 1 - Trace top-level DBI method calls returning with results or errors.
5667 2 - As above, adding tracing of top-level method entry with parameters.
5668 3 - As above, adding some high-level information from the driver
5669 and some internal information from the DBI.
5670 4 - As above, adding more detailed information from the driver.
5671 This is the first level to trace all the rows being fetched.
5672 5 to 15 - As above but with more and more internal information.
5673 Trace level 1 is best for a simple overview of what's happening. Trace
5675 levels 2 thru 4 a good choice for general purpose tracing. Levels 5
5676 and above are best reserved for investigating a specific problem, when
5677 you need to see "inside" the driver and DBI.
5678 The trace output is detailed and typically very useful. Much of the
5680 trace output is formatted using the "neat" function, so strings in the
5681 trace output may be edited and truncated by that function.
5682 Trace Flags
5684 Trace flags are used to enable tracing of specific activities within
5685 the DBI and drivers. The DBI defines some trace flags and drivers can
5686 define others. DBI trace flag names begin with a capital letter and
5687 driver specific names begin with a lowercase letter, as usual.
5688 Currently the DBI defines these trace flags:
5690 ALL - turn on all DBI and driver flags (not recommended)
5692 SQL - trace SQL statements executed
5693 (not yet implemented in DBI but implemented in some DBDs)
5694 CON - trace connection process
5695 ENC - trace encoding (unicode translations etc)
5696 (not yet implemented in DBI but implemented in some DBDs)
5697 DBD - trace only DBD messages
5698 (not implemented by all DBDs yet)
5699 TXN - trace transactions
5700 (not implemented in all DBDs yet)
5701 The "parse_trace_flags" and "parse_trace_flag" methods are used to
5703 convert trace flag names into the corresponding integer bit flags.
5704 Enabling Trace
5706 The "$h->trace" method sets the trace settings for a handle and
5707 "DBI->trace" does the same for the DBI.
5708 In addition to the "trace" method, you can enable the same trace
5710 information, and direct the output to a file, by setting the
5711 "DBI_TRACE" environment variable before starting Perl. See "DBI_TRACE"
5712 for more information.
5713 Finally, you can set, or get, the trace settings for a handle using the
5715 "TraceLevel" attribute.
5716 All of those methods use parse_trace_flags() and so allow you set both
5718 the trace level and multiple trace flags by using a string containing
5719 the trace level and/or flag names separated by vertical bar (""|"") or
5720 comma ("","") characters. For example:
5721 local $h->{TraceLevel} = "3|SQL|foo";
5723 Trace Output
5725 Initially trace output is written to "STDERR". Both the "$h->trace"
5726 and "DBI->trace" methods take an optional $trace_file parameter, which
5727 may be either the name of a file to be opened by DBI in append mode, or
5728 a reference to an existing writable (possibly layered) filehandle. If
5729 $trace_file is a filename, and can be opened in append mode, or
5730 $trace_file is a writable filehandle, then all trace output (currently
5731 including that from other handles) is redirected to that file. A
5732 warning is generated if $trace_file can't be opened or is not writable.
5733 Further calls to trace() without $trace_file do not alter where the
5735 trace output is sent. If $trace_file is undefined, then trace output is
5736 sent to "STDERR" and, if the prior trace was opened with $trace_file as
5737 a filename, the previous trace file is closed; if $trace_file was a
5738 filehandle, the filehandle is not closed.
5739 NOTE: If $trace_file is specified as a filehandle, the filehandle
5741 should not be closed until all DBI operations are completed, or the
5742 application has reset the trace file via another call to "trace()" that
5743 changes the trace file.
5744 Tracing to Layered Filehandles
5746 NOTE:
5747 · Tied filehandles are not currently supported, as tie operations are
5749 not available to the PerlIO methods used by the DBI.
5750 · PerlIO layer support requires Perl version 5.8 or higher.
5752 As of version 5.8, Perl provides the ability to layer various
5754 "disciplines" on an open filehandle via the PerlIO module.
5755 A simple example of using PerlIO layers is to use a scalar as the
5757 output:
5758 my $scalar = '';
5760 open( my $fh, "+>:scalar", \$scalar );
5761 $dbh->trace( 2, $fh );
5762 Now all trace output is simply appended to $scalar.
5764 A more complex application of tracing to a layered filehandle is the
5766 use of a custom layer (Refer to Perlio::via for details on creating
5767 custom PerlIO layers.). Consider an application with the following
5768 logger module:
5769 package MyFancyLogger;
5771 sub new
5773 {
5774 my $self = {};
5775 my $fh;
5776 open $fh, '>', 'fancylog.log';
5777 $self->{_fh} = $fh;
5778 $self->{_buf} = '';
5779 return bless $self, shift;
5780 }
5781 sub log
5783 {
5784 my $self = shift;
5785 return unless exists $self->{_fh};
5786 my $fh = $self->{_fh};
5787 $self->{_buf} .= shift;
5788 #
5789 # DBI feeds us pieces at a time, so accumulate a complete line
5790 # before outputing
5791 #
5792 print $fh "At ", scalar localtime(), ':', $self->{_buf}, "\n" and
5793 $self->{_buf} = ''
5794 if $self->{_buf}=~tr/\n//;
5795 }
5796 sub close {
5798 my $self = shift;
5799 return unless exists $self->{_fh};
5800 my $fh = $self->{_fh};
5801 print $fh "At ", scalar localtime(), ':', $self->{_buf}, "\n" and
5802 $self->{_buf} = ''
5803 if $self->{_buf};
5804 close $fh;
5805 delete $self->{_fh};
5806 }
5807 1;
5809 To redirect DBI traces to this logger requires creating a package for
5811 the layer:
5812 package PerlIO::via::MyFancyLogLayer;
5814 sub PUSHED
5816 {
5817 my ($class,$mode,$fh) = @_;
5818 my $logger;
5819 return bless \$logger,$class;
5820 }
5821 sub OPEN {
5823 my ($self, $path, $mode, $fh) = @_;
5824 #
5825 # $path is actually our logger object
5826 #
5827 $$self = $path;
5828 return 1;
5829 }
5830 sub WRITE
5832 {
5833 my ($self, $buf, $fh) = @_;
5834 $$self->log($buf);
5835 return length($buf);
5836 }
5837 sub CLOSE {
5839 my $self = shift;
5840 $$self->close();
5841 return 0;
5842 }
5843 1;
5845 The application can then cause DBI traces to be routed to the logger
5847 using
5848 use PerlIO::via::MyFancyLogLayer;
5850 open my $fh, '>:via(MyFancyLogLayer)', MyFancyLogger->new();
5852 $dbh->trace('SQL', $fh);
5854 Now all trace output will be processed by MyFancyLogger's log() method.
5856 Trace Content
5858 Many of the values embedded in trace output are formatted using the
5859 neat() utility function. This means they may be quoted, sanitized, and
5860 possibly truncated if longer than $DBI::neat_maxlen. See "neat" for
5861 more details.
5862 Tracing Tips
5864 You can add tracing to your own application code using the "trace_msg"
5865 method.
5866 It can sometimes be handy to compare trace files from two different
5868 runs of the same script. However using a tool like "diff" on the
5869 original log output doesn't work well because the trace file is full of
5870 object addresses that may differ on each run.
5871 The DBI includes a handy utility called dbilogstrip that can be used to
5873 'normalize' the log content. It can be used as a filter like this:
5874 DBI_TRACE=2 perl yourscript.pl ...args1... 2>&1 | dbilogstrip > dbitrace1.log
5876 DBI_TRACE=2 perl yourscript.pl ...args2... 2>&1 | dbilogstrip > dbitrace2.log
5877 diff -u dbitrace1.log dbitrace2.log
5878 See dbilogstrip for more information.
5880
5882 The DBI module recognizes a number of environment variables, but most
5883 of them should not be used most of the time. It is better to be
5884 explicit about what you are doing to avoid the need for environment
5885 variables, especially in a web serving system where web servers are
5886 stingy about which environment variables are available.
5887 DBI_DSN
5889 The DBI_DSN environment variable is used by DBI->connect if you do not
5890 specify a data source when you issue the connect. It should have a
5891 format such as "dbi:Driver:databasename".
5892 DBI_DRIVER
5894 The DBI_DRIVER environment variable is used to fill in the database
5895 driver name in DBI->connect if the data source string starts "dbi::"
5896 (thereby omitting the driver). If DBI_DSN omits the driver name,
5897 DBI_DRIVER can fill the gap.
5898 DBI_AUTOPROXY
5900 The DBI_AUTOPROXY environment variable takes a string value that starts
5901 "dbi:Proxy:" and is typically followed by "hostname=...;port=...". It
5902 is used to alter the behaviour of DBI->connect. For full details, see
5903 DBI::Proxy documentation.
5904 DBI_USER
5906 The DBI_USER environment variable takes a string value that is used as
5907 the user name if the DBI->connect call is given undef (as distinct from
5908 an empty string) as the username argument. Be wary of the security
5909 implications of using this.
5910 DBI_PASS
5912 The DBI_PASS environment variable takes a string value that is used as
5913 the password if the DBI->connect call is given undef (as distinct from
5914 an empty string) as the password argument. Be extra wary of the
5915 security implications of using this.
5916 DBI_DBNAME (obsolete)
5918 The DBI_DBNAME environment variable takes a string value that is used
5919 only when the obsolescent style of DBI->connect (with driver name as
5920 fourth parameter) is used, and when no value is provided for the first
5921 (database name) argument.
5922 DBI_TRACE
5924 The DBI_TRACE environment variable specifies the global default trace
5925 settings for the DBI at startup. Can also be used to direct trace
5926 output to a file. When the DBI is loaded it does:
5927 DBI->trace(split /=/, $ENV{DBI_TRACE}, 2) if $ENV{DBI_TRACE};
5929 So if "DBI_TRACE" contains an ""="" character then what follows it is
5931 used as the name of the file to append the trace to.
5932 output appended to that file. If the name begins with a number followed
5934 by an equal sign ("="), then the number and the equal sign are stripped
5935 off from the name, and the number is used to set the trace level. For
5936 example:
5937 DBI_TRACE=1=dbitrace.log perl your_test_script.pl
5939 On Unix-like systems using a Bourne-like shell, you can do this easily
5941 on the command line:
5942 DBI_TRACE=2 perl your_test_script.pl
5944 See "TRACING" for more information.
5946 PERL_DBI_DEBUG (obsolete)
5948 An old variable that should no longer be used; equivalent to DBI_TRACE.
5949 DBI_PROFILE
5951 The DBI_PROFILE environment variable can be used to enable profiling of
5952 DBI method calls. See DBI::Profile for more information.
5953 DBI_PUREPERL
5955 The DBI_PUREPERL environment variable can be used to enable the use of
5956 DBI::PurePerl. See DBI::PurePerl for more information.
5957
5959 Fatal Errors
5960 Can't call method "prepare" without a package or object reference
5961 The $dbh handle you're using to call "prepare" is probably
5962 undefined because the preceding "connect" failed. You should always
5963 check the return status of DBI methods, or use the "RaiseError"
5964 attribute.
5965 Can't call method "execute" without a package or object reference
5967 The $sth handle you're using to call "execute" is probably
5968 undefined because the preceding "prepare" failed. You should always
5969 check the return status of DBI methods, or use the "RaiseError"
5970 attribute.
5971 DBI/DBD internal version mismatch
5973 The DBD driver module was built with a different version of DBI
5974 than the one currently being used. You should rebuild the DBD
5975 module under the current version of DBI.
5976 (Some rare platforms require "static linking". On those platforms,
5978 there may be an old DBI or DBD driver version actually embedded in
5979 the Perl executable being used.)
5980 DBD driver has not implemented the AutoCommit attribute
5982 The DBD driver implementation is incomplete. Consult the author.
5983 Can't [sg]et %s->{%s}: unrecognised attribute
5985 You attempted to set or get an unknown attribute of a handle. Make
5986 sure you have spelled the attribute name correctly; case is
5987 significant (e.g., "Autocommit" is not the same as "AutoCommit").
5988
5990 A pure-perl emulation of the DBI is included in the distribution for
5991 people using pure-perl drivers who, for whatever reason, can't install
5992 the compiled DBI. See DBI::PurePerl.
5993
5995 Driver and Database Documentation
5996 Refer to the documentation for the DBD driver that you are using.
5997 Refer to the SQL Language Reference Manual for the database engine that
5999 you are using.
6000 ODBC and SQL/CLI Standards Reference Information
6002 More detailed information about the semantics of certain DBI methods
6003 that are based on ODBC and SQL/CLI standards is available on-line via
6004 microsoft.com, for ODBC, and www.jtc1sc32.org for the SQL/CLI standard:
6005 DBI method ODBC function SQL/CLI Working Draft
6007 ---------- ------------- ---------------------
6008 column_info SQLColumns Page 124
6009 foreign_key_info SQLForeignKeys Page 163
6010 get_info SQLGetInfo Page 214
6011 primary_key_info SQLPrimaryKeys Page 254
6012 table_info SQLTables Page 294
6013 type_info SQLGetTypeInfo Page 239
6014 statistics_info SQLStatistics
6015 To find documentation on the ODBC function you can use the MSDN search
6017 facility at:
6018 http://msdn.microsoft.com/Search
6020 and search for something like "SQLColumns returns".
6022 And for SQL/CLI standard information on SQLColumns you'd read page 124
6024 of the (very large) SQL/CLI Working Draft available from:
6025 http://jtc1sc32.org/doc/N0701-0750/32N0744T.pdf
6027 Standards Reference Information
6029 A hyperlinked, browsable version of the BNF syntax for SQL92 (plus
6030 Oracle 7 SQL and PL/SQL) is available here:
6031 http://cui.unige.ch/db-research/Enseignement/analyseinfo/SQL92/BNFindex.html
6033 You can find more information about SQL standards online by searching
6035 for the appropriate standard names and numbers. For example, searching
6036 for "ANSI/ISO/IEC International Standard (IS) Database Language SQL -
6037 Part 1: SQL/Framework" you'll find a copy at:
6038 ftp://ftp.iks-jena.de/mitarb/lutz/standards/sql/ansi-iso-9075-1-1999.pdf
6040 Books and Articles
6042 Programming the Perl DBI, by Alligator Descartes and Tim Bunce.
6043 <http://books.perl.org/book/154>
6044 Programming Perl 3rd Ed. by Larry Wall, Tom Christiansen & Jon Orwant.
6046 <http://books.perl.org/book/134>
6047 Learning Perl by Randal Schwartz. <http://books.perl.org/book/101>
6049 Details of many other books related to perl can be found at
6051 <http://books.perl.org>
6052 Perl Modules
6054 Index of DBI related modules available from CPAN:
6055 L<https://metacpan.org/search?q=DBD%3A%3A>
6057 L<https://metacpan.org/search?q=DBIx%3A%3A>
6058 L<https://metacpan.org/search?q=DBI>
6059 For a good comparison of RDBMS-OO mappers and some OO-RDBMS mappers
6061 (including Class::DBI, Alzabo, and DBIx::RecordSet in the former
6062 category and Tangram and SPOPS in the latter) see the Perl Object-
6063 Oriented Persistence project pages at:
6064 http://poop.sourceforge.net
6066 A similar page for Java toolkits can be found at:
6068 http://c2.com/cgi-bin/wiki?ObjectRelationalToolComparison
6070 Mailing List
6072 The dbi-users mailing list is the primary means of communication among
6073 users of the DBI and its related modules. For details send email to:
6074 L<dbi-users-help@perl.org>
6076 There are typically between 700 and 900 messages per month. You have
6078 to subscribe in order to be able to post. However you can opt for a
6079 'post-only' subscription.
6080 Mailing list archives (of variable quality) are held at:
6082 http://groups.google.com/groups?group=perl.dbi.users
6084 http://www.xray.mpe.mpg.de/mailing-lists/dbi/
6085 http://www.mail-archive.com/dbi-users%40perl.org/
6086 Assorted Related Links
6088 The DBI "Home Page":
6089 http://dbi.perl.org/
6091 Other DBI related links:
6093 http://www.perlmonks.org/?node=DBI%20recipes
6095 http://www.perlmonks.org/?node=Speeding%20up%20the%20DBI
6096 Other database related links:
6098 http://www.connectionstrings.com/
6100 Security, especially the "SQL Injection" attack:
6102 http://bobby-tables.com/
6104 http://online.securityfocus.com/infocus/1644
6105 FAQ
6107 See <http://faq.dbi-support.com/>
6108
6110 DBI by Tim Bunce, <http://www.tim.bunce.name>
6111 This pod text by Tim Bunce, J. Douglas Dunlop, Jonathan Leffler and
6113 others. Perl by Larry Wall and the "perl5-porters".
6114
6116 The DBI module is Copyright (c) 1994-2012 Tim Bunce. Ireland. All
6117 rights reserved.
6118 You may distribute under the terms of either the GNU General Public
6120 License or the Artistic License, as specified in the Perl 5.10.0 README
6121 file.
6122
6124 The DBI is free Open Source software. IT COMES WITHOUT WARRANTY OF ANY
6125 KIND.
6126 Support
6128 My consulting company, Data Plan Services, offers annual and multi-
6129 annual support contracts for the DBI. These provide sustained support
6130 for DBI development, and sustained value for you in return. Contact me
6131 for details.
6132 Sponsor Enhancements
6134 If your company would benefit from a specific new DBI feature, please
6135 consider sponsoring its development. Work is performed rapidly, and
6136 usually on a fixed-price payment-on-delivery basis. Contact me for
6137 details.
6138 Using such targeted financing allows you to contribute to DBI
6140 development, and rapidly get something specific and valuable in return.
6141
6143 I would like to acknowledge the valuable contributions of the many
6144 people I have worked with on the DBI project, especially in the early
6145 years (1992-1994). In no particular order: Kevin Stock, Buzz Moschetti,
6146 Kurt Andersen, Ted Lemon, William Hails, Garth Kennedy, Michael
6147 Peppler, Neil S. Briscoe, Jeff Urlwin, David J. Hughes, Jeff Stander,
6148 Forrest D Whitcher, Larry Wall, Jeff Fried, Roy Johnson, Paul Hudson,
6149 Georg Rehfeld, Steve Sizemore, Ron Pool, Jon Meek, Tom Christiansen,
6150 Steve Baumgarten, Randal Schwartz, and a whole lot more.
6151 Then, of course, there are the poor souls who have struggled through
6153 untold and undocumented obstacles to actually implement DBI drivers.
6154 Among their ranks are Jochen Wiedmann, Alligator Descartes, Jonathan
6155 Leffler, Jeff Urlwin, Michael Peppler, Henrik Tougaard, Edwin Pratomo,
6156 Davide Migliavacca, Jan Pazdziora, Peter Haworth, Edmund Mergl, Steve
6157 Williams, Thomas Lowery, and Phlip Plumlee. Without them, the DBI would
6158 not be the practical reality it is today. I'm also especially grateful
6159 to Alligator Descartes for starting work on the first edition of the
6160 "Programming the Perl DBI" book and letting me jump on board.
6161 The DBI and DBD::Oracle were originally developed while I was Technical
6163 Director (CTO) of the Paul Ingram Group in the UK. So I'd especially
6164 like to thank Paul for his generosity and vision in supporting this
6165 work for many years.
6166 A couple of specific DBI features have been sponsored by enlightened
6168 companies:
6169 The development of the swap_inner_handle() method was sponsored by
6171 BizRate.com (<http://BizRate.com>)
6172 The development of DBD::Gofer and related modules was sponsored by
6174 Shopzilla.com (<http://Shopzilla.com>), where I currently work.
6175
6177 As you can see above, many people have contributed to the DBI and
6178 drivers in many ways over many years.
6179 If you'd like to help then see <http://dbi.perl.org/contributing>.
6181 If you'd like the DBI to do something new or different then a good way
6183 to make that happen is to do it yourself and send me a patch to the
6184 source code that shows the changes. (But read "Speak before you patch"
6185 below.)
6186 Browsing the source code repository
6188 Use https://github.com/perl5-dbi/dbi
6189 How to create a patch using Git
6191 The DBI source code is maintained using Git. To access the source
6192 you'll need to install a Git client. Then, to get the source code, do:
6193 git clone https://github.com/perl5-dbi/dbi.git DBI-git
6195 The source code will now be available in the new subdirectory
6197 "DBI-git".
6198 When you want to synchronize later, issue the command
6200 git pull --all
6202 Make your changes, test them, test them again until everything passes.
6204 If there are no tests for the new feature you added or a behaviour
6205 change, the change should include a new test. Then commit the changes.
6206 Either use
6207 git gui
6209 or
6211 git commit -a -m 'Message to my changes'
6213 If you get any conflicts reported you'll need to fix them first.
6215 Then generate the patch file to be mailed:
6217 git format-patch -1 --attach
6219 which will create a file 0001-*.patch (where * relates to the commit
6221 message). Read the patch file, as a sanity check, and then email it to
6222 dbi-dev@perl.org.
6223 If you have a github <https://github.com> account, you can also fork
6225 the repository, commit your changes to the forked repository and then
6226 do a pull request.
6227 How to create a patch without Git
6229 Unpack a fresh copy of the distribution:
6230 wget http://cpan.metacpan.org/authors/id/T/TI/TIMB/DBI-1.627.tar.gz
6232 tar xfz DBI-1.627.tar.gz
6233 Rename the newly created top level directory:
6235 mv DBI-1.627 DBI-1.627.your_foo
6237 Edit the contents of DBI-1.627.your_foo/* till it does what you want.
6239 Test your changes and then remove all temporary files:
6241 make test && make distclean
6243 Go back to the directory you originally unpacked the distribution:
6245 cd ..
6247 Unpack another copy of the original distribution you started with:
6249 tar xfz DBI-1.627.tar.gz
6251 Then create a patch file by performing a recursive "diff" on the two
6253 top level directories:
6254 diff -purd DBI-1.627 DBI-1.627.your_foo > DBI-1.627.your_foo.patch
6256 Speak before you patch
6258 For anything non-trivial or possibly controversial it's a good idea to
6259 discuss (on dbi-dev@perl.org) the changes you propose before actually
6260 spending time working on them. Otherwise you run the risk of them being
6261 rejected because they don't fit into some larger plans you may not be
6262 aware of.
6263 You can also reach the developers on IRC (chat). If they are on-line,
6265 the most likely place to talk to them is the #dbi channel on
6266 irc.perl.org
6267
6269 A German translation of this manual (possibly slightly out of date) is
6270 available, thanks to O'Reilly, at:
6271 http://www.oreilly.de/catalog/perldbiger/
6273
6275 Apache::DBI
6276 To be used with the Apache daemon together with an embedded Perl
6277 interpreter like "mod_perl". Establishes a database connection
6278 which remains open for the lifetime of the HTTP daemon. This way
6279 the CGI connect and disconnect for every database access becomes
6280 superfluous.
6281 SQL Parser
6283 See also the SQL::Statement module, SQL parser and engine.
6284perl v5.30.0 2019-07-26 DBI(3)