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 1.641
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 = $dbh->last_insert_id($catalog, $schema, $table, $field);
2495 $rv = $dbh->last_insert_id($catalog, $schema, $table, $field, \%attr);
2496 Returns a value 'identifying' the row just inserted, if possible.
2498 Typically this would be a value assigned by the database server to a
2499 column with an auto_increment or serial type. Returns undef if the
2500 driver does not support the method or can't determine the value.
2501 The $catalog, $schema, $table, and $field parameters may be required
2503 for some drivers (see below). If you don't know the parameter values
2504 and your driver does not need them, then use "undef" for each.
2505 There are several caveats to be aware of with this method if you want
2507 to use it for portable applications:
2508 * For some drivers the value may only available immediately after the
2510 insert statement has executed (e.g., mysql, Informix).
2511 * For some drivers the $catalog, $schema, $table, and $field parameters
2513 are required, for others they are ignored (e.g., mysql).
2514 * Drivers may return an indeterminate value if no insert has been
2516 performed yet.
2517 * For some drivers the value may only be available if placeholders have
2519 not been used (e.g., Sybase, MS SQL). In this case the value returned
2520 would be from the last non-placeholder insert statement.
2521 * Some drivers may need driver-specific hints about how to get the
2523 value. For example, being told the name of the database 'sequence'
2524 object that holds the value. Any such hints are passed as driver-
2525 specific attributes in the \%attr parameter.
2526 * If the underlying database offers nothing better, then some drivers
2528 may attempt to implement this method by executing ""select max($field)
2529 from $table"". Drivers using any approach like this should issue a
2530 warning if "AutoCommit" is true because it is generally unsafe -
2531 another process may have modified the table between your insert and the
2532 select. For situations where you know it is safe, such as when you have
2533 locked the table, you can silence the warning by passing "Warn" => 0 in
2534 \%attr.
2535 * If no insert has been performed yet, or the last insert failed, then
2537 the value is implementation defined.
2538 Given all the caveats above, it's clear that this method must be used
2540 with care.
2541 The "last_insert_id" method was added in DBI 1.38.
2543 "selectrow_array"
2545 @row_ary = $dbh->selectrow_array($statement);
2547 @row_ary = $dbh->selectrow_array($statement, \%attr);
2548 @row_ary = $dbh->selectrow_array($statement, \%attr, @bind_values);
2549 This utility method combines "prepare", "execute" and "fetchrow_array"
2551 into a single call. If called in a list context, it returns the first
2552 row of data from the statement. The $statement parameter can be a
2553 previously prepared statement handle, in which case the "prepare" is
2554 skipped.
2555 If any method fails, and "RaiseError" is not set, "selectrow_array"
2557 will return an empty list.
2558 If called in a scalar context for a statement handle that has more than
2560 one column, it is undefined whether the driver will return the value of
2561 the first column or the last. So don't do that. Also, in a scalar
2562 context, an "undef" is returned if there are no more rows or if an
2563 error occurred. That "undef" can't be distinguished from an "undef"
2564 returned because the first field value was NULL. For these reasons you
2565 should exercise some caution if you use "selectrow_array" in a scalar
2566 context, or just don't do that.
2567 "selectrow_arrayref"
2569 $ary_ref = $dbh->selectrow_arrayref($statement);
2571 $ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
2572 $ary_ref = $dbh->selectrow_arrayref($statement, \%attr, @bind_values);
2573 This utility method combines "prepare", "execute" and
2575 "fetchrow_arrayref" into a single call. It returns the first row of
2576 data from the statement. The $statement parameter can be a previously
2577 prepared statement handle, in which case the "prepare" is skipped.
2578 If any method fails, and "RaiseError" is not set, "selectrow_arrayref"
2580 will return undef.
2581 "selectrow_hashref"
2583 $hash_ref = $dbh->selectrow_hashref($statement);
2585 $hash_ref = $dbh->selectrow_hashref($statement, \%attr);
2586 $hash_ref = $dbh->selectrow_hashref($statement, \%attr, @bind_values);
2587 This utility method combines "prepare", "execute" and
2589 "fetchrow_hashref" into a single call. It returns the first row of data
2590 from the statement. The $statement parameter can be a previously
2591 prepared statement handle, in which case the "prepare" is skipped.
2592 If any method fails, and "RaiseError" is not set, "selectrow_hashref"
2594 will return undef.
2595 "selectall_arrayref"
2597 $ary_ref = $dbh->selectall_arrayref($statement);
2599 $ary_ref = $dbh->selectall_arrayref($statement, \%attr);
2600 $ary_ref = $dbh->selectall_arrayref($statement, \%attr, @bind_values);
2601 This utility method combines "prepare", "execute" and
2603 "fetchall_arrayref" into a single call. It returns a reference to an
2604 array containing a reference to an array (or hash, see below) for each
2605 row of data fetched.
2606 The $statement parameter can be a previously prepared statement handle,
2608 in which case the "prepare" is skipped. This is recommended if the
2609 statement is going to be executed many times.
2610 If "RaiseError" is not set and any method except "fetchall_arrayref"
2612 fails then "selectall_arrayref" will return "undef"; if
2613 "fetchall_arrayref" fails then it will return with whatever data has
2614 been fetched thus far. You should check "$dbh->err" afterwards (or use
2615 the "RaiseError" attribute) to discover if the data is complete or was
2616 truncated due to an error.
2617 The "fetchall_arrayref" method called by "selectall_arrayref" supports
2619 a $max_rows parameter. You can specify a value for $max_rows by
2620 including a '"MaxRows"' attribute in \%attr. In which case finish() is
2621 called for you after fetchall_arrayref() returns.
2622 The "fetchall_arrayref" method called by "selectall_arrayref" also
2624 supports a $slice parameter. You can specify a value for $slice by
2625 including a '"Slice"' or '"Columns"' attribute in \%attr. The only
2626 difference between the two is that if "Slice" is not defined and
2627 "Columns" is an array ref, then the array is assumed to contain column
2628 index values (which count from 1), rather than perl array index values.
2629 In which case the array is copied and each value decremented before
2630 passing to "/fetchall_arrayref".
2631 You may often want to fetch an array of rows where each row is stored
2633 as a hash. That can be done simply using:
2634 my $emps = $dbh->selectall_arrayref(
2636 "SELECT ename FROM emp ORDER BY ename",
2637 { Slice => {} }
2638 );
2639 foreach my $emp ( @$emps ) {
2640 print "Employee: $emp->{ename}\n";
2641 }
2642 Or, to fetch into an array instead of an array ref:
2644 @result = @{ $dbh->selectall_arrayref($sql, { Slice => {} }) };
2646 See "fetchall_arrayref" method for more details.
2648 "selectall_array"
2650 @ary = $dbh->selectall_array($statement);
2652 @ary = $dbh->selectall_array($statement, \%attr);
2653 @ary = $dbh->selectall_array($statement, \%attr, @bind_values);
2654 This is a convenience wrapper around selectall_arrayref that returns
2656 the rows directly as a list, rather than a reference to an array of
2657 rows.
2658 Note that if "RaiseError" is not set then you can't tell the difference
2660 between returning no rows and an error. Using RaiseError is best
2661 practice.
2662 "selectall_hashref"
2664 $hash_ref = $dbh->selectall_hashref($statement, $key_field);
2666 $hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr);
2667 $hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr, @bind_values);
2668 This utility method combines "prepare", "execute" and
2670 "fetchall_hashref" into a single call. It returns a reference to a hash
2671 containing one entry, at most, for each row, as returned by
2672 fetchall_hashref().
2673 The $statement parameter can be a previously prepared statement handle,
2675 in which case the "prepare" is skipped. This is recommended if the
2676 statement is going to be executed many times.
2677 The $key_field parameter defines which column, or columns, are used as
2679 keys in the returned hash. It can either be the name of a single field,
2680 or a reference to an array containing multiple field names. Using
2681 multiple names yields a tree of nested hashes.
2682 If a row has the same key as an earlier row then it replaces the
2684 earlier row.
2685 If any method except "fetchrow_hashref" fails, and "RaiseError" is not
2687 set, "selectall_hashref" will return "undef". If "fetchrow_hashref"
2688 fails and "RaiseError" is not set, then it will return with whatever
2689 data it has fetched thus far. $DBI::err should be checked to catch
2690 that.
2691 See fetchall_hashref() for more details.
2693 "selectcol_arrayref"
2695 $ary_ref = $dbh->selectcol_arrayref($statement);
2697 $ary_ref = $dbh->selectcol_arrayref($statement, \%attr);
2698 $ary_ref = $dbh->selectcol_arrayref($statement, \%attr, @bind_values);
2699 This utility method combines "prepare", "execute", and fetching one
2701 column from all the rows, into a single call. It returns a reference to
2702 an array containing the values of the first column from each row.
2703 The $statement parameter can be a previously prepared statement handle,
2705 in which case the "prepare" is skipped. This is recommended if the
2706 statement is going to be executed many times.
2707 If any method except "fetch" fails, and "RaiseError" is not set,
2709 "selectcol_arrayref" will return "undef". If "fetch" fails and
2710 "RaiseError" is not set, then it will return with whatever data it has
2711 fetched thus far. $DBI::err should be checked to catch that.
2712 The "selectcol_arrayref" method defaults to pushing a single column
2714 value (the first) from each row into the result array. However, it can
2715 also push another column, or even multiple columns per row, into the
2716 result array. This behaviour can be specified via a '"Columns"'
2717 attribute which must be a ref to an array containing the column number
2718 or numbers to use. For example:
2719 # get array of id and name pairs:
2721 my $ary_ref = $dbh->selectcol_arrayref("select id, name from table", { Columns=>[1,2] });
2722 my %hash = @$ary_ref; # build hash from key-value pairs so $hash{$id} => name
2723 You can specify a maximum number of rows to fetch by including a
2725 '"MaxRows"' attribute in \%attr.
2726 "prepare"
2728 $sth = $dbh->prepare($statement) or die $dbh->errstr;
2730 $sth = $dbh->prepare($statement, \%attr) or die $dbh->errstr;
2731 Prepares a statement for later execution by the database engine and
2733 returns a reference to a statement handle object.
2734 The returned statement handle can be used to get attributes of the
2736 statement and invoke the "execute" method. See "Statement Handle
2737 Methods".
2738 Drivers for engines without the concept of preparing a statement will
2740 typically just store the statement in the returned handle and process
2741 it when "$sth->execute" is called. Such drivers are unlikely to give
2742 much useful information about the statement, such as
2743 "$sth->{NUM_OF_FIELDS}", until after "$sth->execute" has been called.
2744 Portable applications should take this into account.
2745 In general, DBI drivers do not parse the contents of the statement
2747 (other than simply counting any Placeholders). The statement is passed
2748 directly to the database engine, sometimes known as pass-thru mode.
2749 This has advantages and disadvantages. On the plus side, you can access
2750 all the functionality of the engine being used. On the downside, you're
2751 limited if you're using a simple engine, and you need to take extra
2752 care if writing applications intended to be portable between engines.
2753 Portable applications should not assume that a new statement can be
2755 prepared and/or executed while still fetching results from a previous
2756 statement.
2757 Some command-line SQL tools use statement terminators, like a
2759 semicolon, to indicate the end of a statement. Such terminators should
2760 not normally be used with the DBI.
2761 "prepare_cached"
2763 $sth = $dbh->prepare_cached($statement)
2765 $sth = $dbh->prepare_cached($statement, \%attr)
2766 $sth = $dbh->prepare_cached($statement, \%attr, $if_active)
2767 Like "prepare" except that the statement handle returned will be stored
2769 in a hash associated with the $dbh. If another call is made to
2770 "prepare_cached" with the same $statement and %attr parameter values,
2771 then the corresponding cached $sth will be returned without contacting
2772 the database server. Be sure to understand the cautions and caveats
2773 noted below.
2774 The $if_active parameter lets you adjust the behaviour if an already
2776 cached statement handle is still Active. There are several
2777 alternatives:
2778 0: A warning will be generated, and finish() will be called on the
2780 statement handle before it is returned. This is the default behaviour
2781 if $if_active is not passed.
2782 1: finish() will be called on the statement handle, but the warning is
2783 suppressed.
2784 2: Disables any checking.
2785 3: The existing active statement handle will be removed from the cache
2786 and a new statement handle prepared and cached in its place. This is
2787 the safest option because it doesn't affect the state of the old
2788 handle, it just removes it from the cache. [Added in DBI 1.40]
2789 Here are some examples of "prepare_cached":
2791 sub insert_hash {
2793 my ($table, $field_values) = @_;
2794 # sort to keep field order, and thus sql, stable for prepare_cached
2795 my @fields = sort keys %$field_values;
2796 my @values = @{$field_values}{@fields};
2797 my $sql = sprintf "insert into %s (%s) values (%s)",
2798 $table, join(",", @fields), join(",", ("?")x@fields);
2799 my $sth = $dbh->prepare_cached($sql);
2800 return $sth->execute(@values);
2801 }
2802 sub search_hash {
2804 my ($table, $field_values) = @_;
2805 # sort to keep field order, and thus sql, stable for prepare_cached
2806 my @fields = sort keys %$field_values;
2807 my @values = @{$field_values}{@fields};
2808 my $qualifier = "";
2809 $qualifier = "where ".join(" and ", map { "$_=?" } @fields) if @fields;
2810 $sth = $dbh->prepare_cached("SELECT * FROM $table $qualifier");
2811 return $dbh->selectall_arrayref($sth, {}, @values);
2812 }
2813 Caveat emptor: This caching can be useful in some applications, but it
2815 can also cause problems and should be used with care. Here is a
2816 contrived case where caching would cause a significant problem:
2817 my $sth = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
2819 $sth->execute(...);
2820 while (my $data = $sth->fetchrow_hashref) {
2821 # later, in some other code called within the loop...
2823 my $sth2 = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
2824 $sth2->execute(...);
2825 while (my $data2 = $sth2->fetchrow_arrayref) {
2826 do_stuff(...);
2827 }
2828 }
2829 In this example, since both handles are preparing the exact same
2831 statement, $sth2 will not be its own statement handle, but a duplicate
2832 of $sth returned from the cache. The results will certainly not be what
2833 you expect. Typically the inner fetch loop will work normally,
2834 fetching all the records and terminating when there are no more, but
2835 now that $sth is the same as $sth2 the outer fetch loop will also
2836 terminate.
2837 You'll know if you run into this problem because prepare_cached() will
2839 generate a warning by default (when $if_active is false).
2840 The cache used by prepare_cached() is keyed by both the statement and
2842 any attributes so you can also avoid this issue by doing something
2843 like:
2844 $sth = $dbh->prepare_cached("...", { dbi_dummy => __FILE__.__LINE__ });
2846 which will ensure that prepare_cached only returns statements cached by
2848 that line of code in that source file.
2849 Also, to ensure the attributes passed are always the same, avoid
2851 passing references inline. For example, the Slice attribute is
2852 specified as a reference. Be sure to declare it external to the call to
2853 prepare_cached(), such that a new hash reference is not created on
2854 every call. See "connect_cached" for more details and examples.
2855 If you'd like the cache to managed intelligently, you can tie the
2857 hashref returned by "CachedKids" to an appropriate caching module, such
2858 as Tie::Cache::LRU:
2859 my $cache;
2861 tie %$cache, 'Tie::Cache::LRU', 500;
2862 $dbh->{CachedKids} = $cache;
2863 "commit"
2865 $rc = $dbh->commit or die $dbh->errstr;
2867 Commit (make permanent) the most recent series of database changes if
2869 the database supports transactions and AutoCommit is off.
2870 If "AutoCommit" is on, then calling "commit" will issue a "commit
2872 ineffective with AutoCommit" warning.
2873 See also "Transactions" in the "FURTHER INFORMATION" section below.
2875 "rollback"
2877 $rc = $dbh->rollback or die $dbh->errstr;
2879 Rollback (undo) the most recent series of uncommitted database changes
2881 if the database supports transactions and AutoCommit is off.
2882 If "AutoCommit" is on, then calling "rollback" will issue a "rollback
2884 ineffective with AutoCommit" warning.
2885 See also "Transactions" in the "FURTHER INFORMATION" section below.
2887 "begin_work"
2889 $rc = $dbh->begin_work or die $dbh->errstr;
2891 Enable transactions (by turning "AutoCommit" off) until the next call
2893 to "commit" or "rollback". After the next "commit" or "rollback",
2894 "AutoCommit" will automatically be turned on again.
2895 If "AutoCommit" is already off when "begin_work" is called then it does
2897 nothing except return an error. If the driver does not support
2898 transactions then when "begin_work" attempts to set "AutoCommit" off
2899 the driver will trigger a fatal error.
2900 See also "Transactions" in the "FURTHER INFORMATION" section below.
2902 "disconnect"
2904 $rc = $dbh->disconnect or warn $dbh->errstr;
2906 Disconnects the database from the database handle. "disconnect" is
2908 typically only used before exiting the program. The handle is of little
2909 use after disconnecting.
2910 The transaction behaviour of the "disconnect" method is, sadly,
2912 undefined. Some database systems (such as Oracle and Ingres) will
2913 automatically commit any outstanding changes, but others (such as
2914 Informix) will rollback any outstanding changes. Applications not
2915 using "AutoCommit" should explicitly call "commit" or "rollback" before
2916 calling "disconnect".
2917 The database is automatically disconnected by the "DESTROY" method if
2919 still connected when there are no longer any references to the handle.
2920 The "DESTROY" method for each driver should implicitly call "rollback"
2921 to undo any uncommitted changes. This is vital behaviour to ensure that
2922 incomplete transactions don't get committed simply because Perl calls
2923 "DESTROY" on every object before exiting. Also, do not rely on the
2924 order of object destruction during "global destruction", as it is
2925 undefined.
2926 Generally, if you want your changes to be committed or rolled back when
2928 you disconnect, then you should explicitly call "commit" or "rollback"
2929 before disconnecting.
2930 If you disconnect from a database while you still have active statement
2932 handles (e.g., SELECT statement handles that may have more data to
2933 fetch), you will get a warning. The warning may indicate that a fetch
2934 loop terminated early, perhaps due to an uncaught error. To avoid the
2935 warning call the "finish" method on the active handles.
2936 "ping"
2938 $rc = $dbh->ping;
2940 Attempts to determine, in a reasonably efficient way, if the database
2942 server is still running and the connection to it is still working.
2943 Individual drivers should implement this function in the most suitable
2944 manner for their database engine.
2945 The current default implementation always returns true without actually
2947 doing anything. Actually, it returns ""0 but true"" which is true but
2948 zero. That way you can tell if the return value is genuine or just the
2949 default. Drivers should override this method with one that does the
2950 right thing for their type of database.
2951 Few applications would have direct use for this method. See the
2953 specialized Apache::DBI module for one example usage.
2954 "get_info"
2956 $value = $dbh->get_info( $info_type );
2958 Returns information about the implementation, i.e. driver and data
2960 source capabilities, restrictions etc. It returns "undef" for unknown
2961 or unimplemented information types. For example:
2962 $database_version = $dbh->get_info( 18 ); # SQL_DBMS_VER
2964 $max_select_tables = $dbh->get_info( 106 ); # SQL_MAXIMUM_TABLES_IN_SELECT
2965 See "Standards Reference Information" for more detailed information
2967 about the information types and their meanings and possible return
2968 values.
2969 The DBI::Const::GetInfoType module exports a %GetInfoType hash that can
2971 be used to map info type names to numbers. For example:
2972 $database_version = $dbh->get_info( $GetInfoType{SQL_DBMS_VER} );
2974 The names are a merging of the ANSI and ODBC standards (which differ in
2976 some cases). See DBI::Const::GetInfoType for more details.
2977 Because some DBI methods make use of get_info(), drivers are strongly
2979 encouraged to support at least the following very minimal set of
2980 information types to ensure the DBI itself works properly:
2981 Type Name Example A Example B
2983 ---- -------------------------- ------------ ----------------
2984 17 SQL_DBMS_NAME 'ACCESS' 'Oracle'
2985 18 SQL_DBMS_VER '03.50.0000' '08.01.0721 ...'
2986 29 SQL_IDENTIFIER_QUOTE_CHAR '`' '"'
2987 41 SQL_CATALOG_NAME_SEPARATOR '.' '@'
2988 114 SQL_CATALOG_LOCATION 1 2
2989 Values from 9000 to 9999 for get_info are officially reserved for use
2991 by Perl DBI. Values in that range which have been assigned a meaning
2992 are defined here:
2993 9000: true if a backslash character ("\") before placeholder-like text
2995 (e.g. "?", ":foo") will prevent it being treated as a placeholder by
2996 the driver. The backslash will be removed before the text is passed to
2997 the backend.
2998 "table_info"
3000 $sth = $dbh->table_info( $catalog, $schema, $table, $type );
3002 $sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );
3003 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3005 Returns an active statement handle that can be used to fetch
3007 information about tables and views that exist in the database.
3008 The arguments $catalog, $schema and $table may accept search patterns
3010 according to the database/driver, for example: $table = '%FOO%';
3011 Remember that the underscore character ('"_"') is a search pattern that
3012 means match any character, so 'FOO_%' is the same as 'FOO%' and
3013 'FOO_BAR%' will match names like 'FOO1BAR'.
3014 The value of $type is a comma-separated list of one or more types of
3016 tables to be returned in the result set. Each value may optionally be
3017 quoted, e.g.:
3018 $type = "TABLE";
3020 $type = "'TABLE','VIEW'";
3021 In addition the following special cases may also be supported by some
3023 drivers:
3024 · If the value of $catalog is '%' and $schema and $table name are
3026 empty strings, the result set contains a list of catalog names.
3027 For example:
3028 $sth = $dbh->table_info('%', '', '');
3030 · If the value of $schema is '%' and $catalog and $table are empty
3032 strings, the result set contains a list of schema names.
3033 · If the value of $type is '%' and $catalog, $schema, and $table are
3035 all empty strings, the result set contains a list of table types.
3036 If your driver doesn't support one or more of the selection filter
3038 parameters then you may get back more than you asked for and can do the
3039 filtering yourself.
3040 This method can be expensive, and can return a large amount of data.
3042 (For example, small Oracle installation returns over 2000 rows.) So
3043 it's a good idea to use the filters to limit the data as much as
3044 possible.
3045 The statement handle returned has at least the following fields in the
3047 order show below. Other fields, after these, may also be present.
3048 TABLE_CAT: Table catalog identifier. This field is NULL ("undef") if
3050 not applicable to the data source, which is usually the case. This
3051 field is empty if not applicable to the table.
3052 TABLE_SCHEM: The name of the schema containing the TABLE_NAME value.
3054 This field is NULL ("undef") if not applicable to data source, and
3055 empty if not applicable to the table.
3056 TABLE_NAME: Name of the table (or view, synonym, etc).
3058 TABLE_TYPE: One of the following: "TABLE", "VIEW", "SYSTEM TABLE",
3060 "GLOBAL TEMPORARY", "LOCAL TEMPORARY", "ALIAS", "SYNONYM" or a type
3061 identifier that is specific to the data source.
3062 REMARKS: A description of the table. May be NULL ("undef").
3064 Note that "table_info" might not return records for all tables.
3066 Applications can use any valid table regardless of whether it's
3067 returned by "table_info".
3068 See also "tables", "Catalog Methods" and "Standards Reference
3070 Information".
3071 "column_info"
3073 $sth = $dbh->column_info( $catalog, $schema, $table, $column );
3075 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3077 Returns an active statement handle that can be used to fetch
3079 information about columns in specified tables.
3080 The arguments $schema, $table and $column may accept search patterns
3082 according to the database/driver, for example: $table = '%FOO%';
3083 Note: The support for the selection criteria is driver specific. If the
3085 driver doesn't support one or more of them then you may get back more
3086 than you asked for and can do the filtering yourself.
3087 Note: If your driver does not support column_info an undef is returned.
3089 This is distinct from asking for something which does not exist in a
3090 driver which supports column_info as a valid statement handle to an
3091 empty result-set will be returned in this case.
3092 If the arguments don't match any tables then you'll still get a
3094 statement handle, it'll just return no rows.
3095 The statement handle returned has at least the following fields in the
3097 order shown below. Other fields, after these, may also be present.
3098 TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not
3100 applicable to the data source, which is often the case. This field is
3101 empty if not applicable to the table.
3102 TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if
3104 not applicable to the data source, and empty if not applicable to the
3105 table.
3106 TABLE_NAME: The table identifier. Note: A driver may provide column
3108 metadata not only for base tables, but also for derived objects like
3109 SYNONYMS etc.
3110 COLUMN_NAME: The column identifier.
3112 DATA_TYPE: The concise data type code.
3114 TYPE_NAME: A data source dependent data type name.
3116 COLUMN_SIZE: The column size. This is the maximum length in characters
3118 for character data types, the number of digits or bits for numeric data
3119 types or the length in the representation of temporal types. See the
3120 relevant specifications for detailed information.
3121 BUFFER_LENGTH: The length in bytes of transferred data.
3123 DECIMAL_DIGITS: The total number of significant digits to the right of
3125 the decimal point.
3126 NUM_PREC_RADIX: The radix for numeric precision. The value is 10 or 2
3128 for numeric data types and NULL ("undef") if not applicable.
3129 NULLABLE: Indicates if a column can accept NULLs. The following values
3131 are defined:
3132 SQL_NO_NULLS 0
3134 SQL_NULLABLE 1
3135 SQL_NULLABLE_UNKNOWN 2
3136 REMARKS: A description of the column.
3138 COLUMN_DEF: The default value of the column, in a format that can be
3140 used directly in an SQL statement.
3141 Note that this may be an expression and not simply the text used for
3143 the default value in the original CREATE TABLE statement. For example,
3144 given:
3145 col1 char(30) default current_user -- a 'function'
3147 col2 char(30) default 'string' -- a string literal
3148 where "current_user" is the name of a function, the corresponding
3150 "COLUMN_DEF" values would be:
3151 Database col1 col2
3153 -------- ---- ----
3154 Oracle: current_user 'string'
3155 Postgres: "current_user"() 'string'::text
3156 MS SQL: (user_name()) ('string')
3157 SQL_DATA_TYPE: The SQL data type.
3159 SQL_DATETIME_SUB: The subtype code for datetime and interval data
3161 types.
3162 CHAR_OCTET_LENGTH: The maximum length in bytes of a character or binary
3164 data type column.
3165 ORDINAL_POSITION: The column sequence number (starting with 1).
3167 IS_NULLABLE: Indicates if the column can accept NULLs. Possible values
3169 are: 'NO', 'YES' and ''.
3170 SQL/CLI defines the following additional columns:
3172 CHAR_SET_CAT
3174 CHAR_SET_SCHEM
3175 CHAR_SET_NAME
3176 COLLATION_CAT
3177 COLLATION_SCHEM
3178 COLLATION_NAME
3179 UDT_CAT
3180 UDT_SCHEM
3181 UDT_NAME
3182 DOMAIN_CAT
3183 DOMAIN_SCHEM
3184 DOMAIN_NAME
3185 SCOPE_CAT
3186 SCOPE_SCHEM
3187 SCOPE_NAME
3188 MAX_CARDINALITY
3189 DTD_IDENTIFIER
3190 IS_SELF_REF
3191 Drivers capable of supplying any of those values should do so in the
3193 corresponding column and supply undef values for the others.
3194 Drivers wishing to provide extra database/driver specific information
3196 should do so in extra columns beyond all those listed above, and use
3197 lowercase field names with the driver-specific prefix (i.e.,
3198 'ora_...'). Applications accessing such fields should do so by name and
3199 not by column number.
3200 The result set is ordered by TABLE_CAT, TABLE_SCHEM, TABLE_NAME and
3202 ORDINAL_POSITION.
3203 Note: There is some overlap with statement handle attributes (in perl)
3205 and SQLDescribeCol (in ODBC). However, SQLColumns provides more
3206 metadata.
3207 See also "Catalog Methods" and "Standards Reference Information".
3209 "primary_key_info"
3211 $sth = $dbh->primary_key_info( $catalog, $schema, $table );
3213 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3215 Returns an active statement handle that can be used to fetch
3217 information about columns that make up the primary key for a table.
3218 The arguments don't accept search patterns (unlike table_info()).
3219 The statement handle will return one row per column, ordered by
3221 TABLE_CAT, TABLE_SCHEM, TABLE_NAME, and KEY_SEQ. If there is no
3222 primary key then the statement handle will fetch no rows.
3223 Note: The support for the selection criteria, such as $catalog, is
3225 driver specific. If the driver doesn't support catalogs and/or
3226 schemas, it may ignore these criteria.
3227 The statement handle returned has at least the following fields in the
3229 order shown below. Other fields, after these, may also be present.
3230 TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not
3232 applicable to the data source, which is often the case. This field is
3233 empty if not applicable to the table.
3234 TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if
3236 not applicable to the data source, and empty if not applicable to the
3237 table.
3238 TABLE_NAME: The table identifier.
3240 COLUMN_NAME: The column identifier.
3242 KEY_SEQ: The column sequence number (starting with 1). Note: This
3244 field is named ORDINAL_POSITION in SQL/CLI.
3245 PK_NAME: The primary key constraint identifier. This field is NULL
3247 ("undef") if not applicable to the data source.
3248 See also "Catalog Methods" and "Standards Reference Information".
3250 "primary_key"
3252 @key_column_names = $dbh->primary_key( $catalog, $schema, $table );
3254 Simple interface to the primary_key_info() method. Returns a list of
3256 the column names that comprise the primary key of the specified table.
3257 The list is in primary key column sequence order. If there is no
3258 primary key then an empty list is returned.
3259 "foreign_key_info"
3261 $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
3263 , $fk_catalog, $fk_schema, $fk_table );
3264 $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
3266 , $fk_catalog, $fk_schema, $fk_table
3267 , \%attr );
3268 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3270 Returns an active statement handle that can be used to fetch
3272 information about foreign keys in and/or referencing the specified
3273 table(s). The arguments don't accept search patterns (unlike
3274 table_info()).
3275 $pk_catalog, $pk_schema, $pk_table identify the primary (unique) key
3277 table (PKT).
3278 $fk_catalog, $fk_schema, $fk_table identify the foreign key table
3280 (FKT).
3281 If both PKT and FKT are given, the function returns the foreign key, if
3283 any, in table FKT that refers to the primary (unique) key of table PKT.
3284 (Note: In SQL/CLI, the result is implementation-defined.)
3285 If only PKT is given, then the result set contains the primary key of
3287 that table and all foreign keys that refer to it.
3288 If only FKT is given, then the result set contains all foreign keys in
3290 that table and the primary keys to which they refer. (Note: In
3291 SQL/CLI, the result includes unique keys too.)
3292 For example:
3294 $sth = $dbh->foreign_key_info( undef, $user, 'master');
3296 $sth = $dbh->foreign_key_info( undef, undef, undef , undef, $user, 'detail');
3297 $sth = $dbh->foreign_key_info( undef, $user, 'master', undef, $user, 'detail');
3298 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3300 Note: The support for the selection criteria, such as $catalog, is
3302 driver specific. If the driver doesn't support catalogs and/or
3303 schemas, it may ignore these criteria.
3304 The statement handle returned has the following fields in the order
3306 shown below. Because ODBC never includes unique keys, they define
3307 different columns in the result set than SQL/CLI. SQL/CLI column names
3308 are shown in parentheses.
3309 PKTABLE_CAT ( UK_TABLE_CAT ): The primary (unique) key table
3311 catalog identifier. This field is NULL ("undef") if not applicable to
3312 the data source, which is often the case. This field is empty if not
3313 applicable to the table.
3314 PKTABLE_SCHEM ( UK_TABLE_SCHEM ): The primary (unique) key table
3316 schema identifier. This field is NULL ("undef") if not applicable to
3317 the data source, and empty if not applicable to the table.
3318 PKTABLE_NAME ( UK_TABLE_NAME ): The primary (unique) key table
3320 identifier.
3321 PKCOLUMN_NAME (UK_COLUMN_NAME ): The primary (unique) key column
3323 identifier.
3324 FKTABLE_CAT ( FK_TABLE_CAT ): The foreign key table catalog
3326 identifier. This field is NULL ("undef") if not applicable to the data
3327 source, which is often the case. This field is empty if not applicable
3328 to the table.
3329 FKTABLE_SCHEM ( FK_TABLE_SCHEM ): The foreign key table schema
3331 identifier. This field is NULL ("undef") if not applicable to the data
3332 source, and empty if not applicable to the table.
3333 FKTABLE_NAME ( FK_TABLE_NAME ): The foreign key table identifier.
3335 FKCOLUMN_NAME ( FK_COLUMN_NAME ): The foreign key column
3337 identifier.
3338 KEY_SEQ ( ORDINAL_POSITION ): The column sequence number
3340 (starting with 1).
3341 UPDATE_RULE ( UPDATE_RULE ): The referential action for the
3343 UPDATE rule. The following codes are defined:
3344 CASCADE 0
3346 RESTRICT 1
3347 SET NULL 2
3348 NO ACTION 3
3349 SET DEFAULT 4
3350 DELETE_RULE ( DELETE_RULE ): The referential action for the
3352 DELETE rule. The codes are the same as for UPDATE_RULE.
3353 FK_NAME ( FK_NAME ): The foreign key name.
3355 PK_NAME ( UK_NAME ): The primary (unique) key name.
3357 DEFERRABILITY ( DEFERABILITY ): The deferrability of the foreign
3359 key constraint. The following codes are defined:
3360 INITIALLY DEFERRED 5
3362 INITIALLY IMMEDIATE 6
3363 NOT DEFERRABLE 7
3364 ( UNIQUE_OR_PRIMARY ): This column is necessary if a
3366 driver includes all candidate (i.e. primary and alternate) keys in the
3367 result set (as specified by SQL/CLI). The value of this column is
3368 UNIQUE if the foreign key references an alternate key and PRIMARY if
3369 the foreign key references a primary key, or it may be undefined if the
3370 driver doesn't have access to the information.
3371 See also "Catalog Methods" and "Standards Reference Information".
3373 "statistics_info"
3375 Warning: This method is experimental and may change.
3377 $sth = $dbh->statistics_info( $catalog, $schema, $table, $unique_only, $quick );
3379 # then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
3381 Returns an active statement handle that can be used to fetch
3383 statistical information about a table and its indexes.
3384 The arguments don't accept search patterns (unlike "table_info").
3386 If the boolean argument $unique_only is true, only UNIQUE indexes will
3388 be returned in the result set, otherwise all indexes will be returned.
3389 If the boolean argument $quick is set, the actual statistical
3391 information columns (CARDINALITY and PAGES) will only be returned if
3392 they are readily available from the server, and might not be current.
3393 Some databases may return stale statistics or no statistics at all with
3394 this flag set.
3395 The statement handle will return at most one row per column name per
3397 index, plus at most one row for the entire table itself, ordered by
3398 NON_UNIQUE, TYPE, INDEX_QUALIFIER, INDEX_NAME, and ORDINAL_POSITION.
3399 Note: The support for the selection criteria, such as $catalog, is
3401 driver specific. If the driver doesn't support catalogs and/or
3402 schemas, it may ignore these criteria.
3403 The statement handle returned has at least the following fields in the
3405 order shown below. Other fields, after these, may also be present.
3406 TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not
3408 applicable to the data source, which is often the case. This field is
3409 empty if not applicable to the table.
3410 TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if
3412 not applicable to the data source, and empty if not applicable to the
3413 table.
3414 TABLE_NAME: The table identifier.
3416 NON_UNIQUE: Unique index indicator. Returns 0 for unique indexes, 1
3418 for non-unique indexes
3419 INDEX_QUALIFIER: Index qualifier identifier. The identifier that is
3421 used to qualify the index name when doing a "DROP INDEX"; NULL
3422 ("undef") is returned if an index qualifier is not supported by the
3423 data source. If a non-NULL (defined) value is returned in this column,
3424 it must be used to qualify the index name on a "DROP INDEX" statement;
3425 otherwise, the TABLE_SCHEM should be used to qualify the index name.
3426 INDEX_NAME: The index identifier.
3428 TYPE: The type of information being returned. Can be any of the
3430 following values: 'table', 'btree', 'clustered', 'content', 'hashed',
3431 or 'other'.
3432 In the case that this field is 'table', all fields other than
3434 TABLE_CAT, TABLE_SCHEM, TABLE_NAME, TYPE, CARDINALITY, and PAGES will
3435 be NULL ("undef").
3436 ORDINAL_POSITION: Column sequence number (starting with 1).
3438 COLUMN_NAME: The column identifier.
3440 ASC_OR_DESC: Column sort sequence. "A" for Ascending, "D" for
3442 Descending, or NULL ("undef") if not supported for this index.
3443 CARDINALITY: Cardinality of the table or index. For indexes, this is
3445 the number of unique values in the index. For tables, this is the
3446 number of rows in the table. If not supported, the value will be NULL
3447 ("undef").
3448 PAGES: Number of storage pages used by this table or index. If not
3450 supported, the value will be NULL ("undef").
3451 FILTER_CONDITION: The index filter condition as a string. If the index
3453 is not a filtered index, or it cannot be determined whether the index
3454 is a filtered index, this value is NULL ("undef"). If the index is a
3455 filtered index, but the filter condition cannot be determined, this
3456 value is the empty string ''. Otherwise it will be the literal filter
3457 condition as a string, such as "SALARY <= 4500".
3458 See also "Catalog Methods" and "Standards Reference Information".
3460 "tables"
3462 @names = $dbh->tables( $catalog, $schema, $table, $type );
3464 @names = $dbh->tables; # deprecated
3465 Simple interface to table_info(). Returns a list of matching table
3467 names, possibly including a catalog/schema prefix.
3468 See "table_info" for a description of the parameters.
3470 If "$dbh->get_info(29)" returns true (29 is SQL_IDENTIFIER_QUOTE_CHAR)
3472 then the table names are constructed and quoted by "quote_identifier"
3473 to ensure they are usable even if they contain whitespace or reserved
3474 words etc. This means that the table names returned will include quote
3475 characters.
3476 "type_info_all"
3478 $type_info_all = $dbh->type_info_all;
3480 Returns a reference to an array which holds information about each data
3482 type variant supported by the database and driver. The array and its
3483 contents should be treated as read-only.
3484 The first item is a reference to an 'index' hash of "Name ="> "Index"
3486 pairs. The items following that are references to arrays, one per
3487 supported data type variant. The leading index hash defines the names
3488 and order of the fields within the arrays that follow it. For example:
3489 $type_info_all = [
3491 { TYPE_NAME => 0,
3492 DATA_TYPE => 1,
3493 COLUMN_SIZE => 2, # was PRECISION originally
3494 LITERAL_PREFIX => 3,
3495 LITERAL_SUFFIX => 4,
3496 CREATE_PARAMS => 5,
3497 NULLABLE => 6,
3498 CASE_SENSITIVE => 7,
3499 SEARCHABLE => 8,
3500 UNSIGNED_ATTRIBUTE=> 9,
3501 FIXED_PREC_SCALE => 10, # was MONEY originally
3502 AUTO_UNIQUE_VALUE => 11, # was AUTO_INCREMENT originally
3503 LOCAL_TYPE_NAME => 12,
3504 MINIMUM_SCALE => 13,
3505 MAXIMUM_SCALE => 14,
3506 SQL_DATA_TYPE => 15,
3507 SQL_DATETIME_SUB => 16,
3508 NUM_PREC_RADIX => 17,
3509 INTERVAL_PRECISION=> 18,
3510 },
3511 [ 'VARCHAR', SQL_VARCHAR,
3512 undef, "'","'", undef,0, 1,1,0,0,0,undef,1,255, undef
3513 ],
3514 [ 'INTEGER', SQL_INTEGER,
3515 undef, "", "", undef,0, 0,1,0,0,0,undef,0, 0, 10
3516 ],
3517 ];
3518 More than one row may have the same value in the "DATA_TYPE" field if
3520 there are different ways to spell the type name and/or there are
3521 variants of the type with different attributes (e.g., with and without
3522 "AUTO_UNIQUE_VALUE" set, with and without "UNSIGNED_ATTRIBUTE", etc).
3523 The rows are ordered by "DATA_TYPE" first and then by how closely each
3525 type maps to the corresponding ODBC SQL data type, closest first.
3526 The meaning of the fields is described in the documentation for the
3528 "type_info" method.
3529 An 'index' hash is provided so you don't need to rely on index values
3531 defined above. However, using DBD::ODBC with some old ODBC drivers may
3532 return older names, shown as comments in the example above. Another
3533 issue with the index hash is that the lettercase of the keys is not
3534 defined. It is usually uppercase, as show here, but drivers may return
3535 names with any lettercase.
3536 Drivers are also free to return extra driver-specific columns of
3538 information - though it's recommended that they start at column index
3539 50 to leave room for expansion of the DBI/ODBC specification.
3540 The type_info_all() method is not normally used directly. The
3542 "type_info" method provides a more usable and useful interface to the
3543 data.
3544 "type_info"
3546 @type_info = $dbh->type_info($data_type);
3548 Returns a list of hash references holding information about one or more
3550 variants of $data_type. The list is ordered by "DATA_TYPE" first and
3551 then by how closely each type maps to the corresponding ODBC SQL data
3552 type, closest first. If called in a scalar context then only the first
3553 (best) element is returned.
3554 If $data_type is undefined or "SQL_ALL_TYPES", then the list will
3556 contain hashes for all data type variants supported by the database and
3557 driver.
3558 If $data_type is an array reference then "type_info" returns the
3560 information for the first type in the array that has any matches.
3561 The keys of the hash follow the same letter case conventions as the
3563 rest of the DBI (see "Naming Conventions and Name Space"). The
3564 following uppercase items should always exist, though may be undef:
3565 TYPE_NAME (string)
3567 Data type name for use in CREATE TABLE statements etc.
3568 DATA_TYPE (integer)
3570 SQL data type number.
3571 COLUMN_SIZE (integer)
3573 For numeric types, this is either the total number of digits (if
3574 the NUM_PREC_RADIX value is 10) or the total number of bits allowed
3575 in the column (if NUM_PREC_RADIX is 2).
3576 For string types, this is the maximum size of the string in
3578 characters.
3579 For date and interval types, this is the maximum number of
3581 characters needed to display the value.
3582 LITERAL_PREFIX (string)
3584 Characters used to prefix a literal. A typical prefix is ""'"" for
3585 characters, or possibly ""0x"" for binary values passed as
3586 hexadecimal. NULL ("undef") is returned for data types for which
3587 this is not applicable.
3588 LITERAL_SUFFIX (string)
3590 Characters used to suffix a literal. Typically ""'"" for
3591 characters. NULL ("undef") is returned for data types where this
3592 is not applicable.
3593 CREATE_PARAMS (string)
3595 Parameter names for data type definition. For example,
3596 "CREATE_PARAMS" for a "DECIMAL" would be ""precision,scale"" if the
3597 DECIMAL type should be declared as "DECIMAL("precision,scale")"
3598 where precision and scale are integer values. For a "VARCHAR" it
3599 would be ""max length"". NULL ("undef") is returned for data types
3600 for which this is not applicable.
3601 NULLABLE (integer)
3603 Indicates whether the data type accepts a NULL value: 0 or an empty
3604 string = no, 1 = yes, 2 = unknown.
3605 CASE_SENSITIVE (boolean)
3607 Indicates whether the data type is case sensitive in collations and
3608 comparisons.
3609 SEARCHABLE (integer)
3611 Indicates how the data type can be used in a WHERE clause, as
3612 follows:
3613 0 - Cannot be used in a WHERE clause
3615 1 - Only with a LIKE predicate
3616 2 - All comparison operators except LIKE
3617 3 - Can be used in a WHERE clause with any comparison operator
3618 UNSIGNED_ATTRIBUTE (boolean)
3620 Indicates whether the data type is unsigned. NULL ("undef") is
3621 returned for data types for which this is not applicable.
3622 FIXED_PREC_SCALE (boolean)
3624 Indicates whether the data type always has the same precision and
3625 scale (such as a money type). NULL ("undef") is returned for data
3626 types for which this is not applicable.
3627 AUTO_UNIQUE_VALUE (boolean)
3629 Indicates whether a column of this data type is automatically set
3630 to a unique value whenever a new row is inserted. NULL ("undef")
3631 is returned for data types for which this is not applicable.
3632 LOCAL_TYPE_NAME (string)
3634 Localized version of the "TYPE_NAME" for use in dialog with users.
3635 NULL ("undef") is returned if a localized name is not available (in
3636 which case "TYPE_NAME" should be used).
3637 MINIMUM_SCALE (integer)
3639 The minimum scale of the data type. If a data type has a fixed
3640 scale, then "MAXIMUM_SCALE" holds the same value. NULL ("undef")
3641 is returned for data types for which this is not applicable.
3642 MAXIMUM_SCALE (integer)
3644 The maximum scale of the data type. If a data type has a fixed
3645 scale, then "MINIMUM_SCALE" holds the same value. NULL ("undef")
3646 is returned for data types for which this is not applicable.
3647 SQL_DATA_TYPE (integer)
3649 This column is the same as the "DATA_TYPE" column, except for
3650 interval and datetime data types. For interval and datetime data
3651 types, the "SQL_DATA_TYPE" field will return "SQL_INTERVAL" or
3652 "SQL_DATETIME", and the "SQL_DATETIME_SUB" field below will return
3653 the subcode for the specific interval or datetime data type. If
3654 this field is NULL, then the driver does not support or report on
3655 interval or datetime subtypes.
3656 SQL_DATETIME_SUB (integer)
3658 For interval or datetime data types, where the "SQL_DATA_TYPE"
3659 field above is "SQL_INTERVAL" or "SQL_DATETIME", this field will
3660 hold the subcode for the specific interval or datetime data type.
3661 Otherwise it will be NULL ("undef").
3662 Although not mentioned explicitly in the standards, it seems there
3664 is a simple relationship between these values:
3665 DATA_TYPE == (10 * SQL_DATA_TYPE) + SQL_DATETIME_SUB
3667 NUM_PREC_RADIX (integer)
3669 The radix value of the data type. For approximate numeric types,
3670 "NUM_PREC_RADIX" contains the value 2 and "COLUMN_SIZE" holds the
3671 number of bits. For exact numeric types, "NUM_PREC_RADIX" contains
3672 the value 10 and "COLUMN_SIZE" holds the number of decimal digits.
3673 NULL ("undef") is returned either for data types for which this is
3674 not applicable or if the driver cannot report this information.
3675 INTERVAL_PRECISION (integer)
3677 The interval leading precision for interval types. NULL is returned
3678 either for data types for which this is not applicable or if the
3679 driver cannot report this information.
3680 For example, to find the type name for the fields in a select statement
3682 you can do:
3683 @names = map { scalar $dbh->type_info($_)->{TYPE_NAME} } @{ $sth->{TYPE} }
3685 Since DBI and ODBC drivers vary in how they map their types into the
3687 ISO standard types you may need to search for more than one type.
3688 Here's an example looking for a usable type to store a date:
3689 $my_date_type = $dbh->type_info( [ SQL_DATE, SQL_TIMESTAMP ] );
3691 Similarly, to more reliably find a type to store small integers, you
3693 could use a list starting with "SQL_SMALLINT", "SQL_INTEGER",
3694 "SQL_DECIMAL", etc.
3695 See also "Standards Reference Information".
3697 "quote"
3699 $sql = $dbh->quote($value);
3701 $sql = $dbh->quote($value, $data_type);
3702 Quote a string literal for use as a literal value in an SQL statement,
3704 by escaping any special characters (such as quotation marks) contained
3705 within the string and adding the required type of outer quotation
3706 marks.
3707 $sql = sprintf "SELECT foo FROM bar WHERE baz = %s",
3709 $dbh->quote("Don't");
3710 For most database types, at least those that conform to SQL standards,
3712 quote would return 'Don''t' (including the outer quotation marks). For
3713 others it may return something like 'Don\'t'
3714 An undefined $value value will be returned as the string "NULL"
3716 (without single quotation marks) to match how NULLs are represented in
3717 SQL.
3718 If $data_type is supplied, it is used to try to determine the required
3720 quoting behaviour by using the information returned by "type_info". As
3721 a special case, the standard numeric types are optimized to return
3722 $value without calling "type_info".
3723 Quote will probably not be able to deal with all possible input (such
3725 as binary data or data containing newlines), and is not related in any
3726 way with escaping or quoting shell meta-characters.
3727 It is valid for the quote() method to return an SQL expression that
3729 evaluates to the desired string. For example:
3730 $quoted = $dbh->quote("one\ntwo\0three")
3732 may return something like:
3734 CONCAT('one', CHAR(12), 'two', CHAR(0), 'three')
3736 The quote() method should not be used with "Placeholders and Bind
3738 Values".
3739 "quote_identifier"
3741 $sql = $dbh->quote_identifier( $name );
3743 $sql = $dbh->quote_identifier( $catalog, $schema, $table, \%attr );
3744 Quote an identifier (table name etc.) for use in an SQL statement, by
3746 escaping any special characters (such as double quotation marks) it
3747 contains and adding the required type of outer quotation marks.
3748 Undefined names are ignored and the remainder are quoted and then
3750 joined together, typically with a dot (".") character. For example:
3751 $id = $dbh->quote_identifier( undef, 'Her schema', 'My table' );
3753 would, for most database types, return "Her schema"."My table"
3755 (including all the double quotation marks).
3756 If three names are supplied then the first is assumed to be a catalog
3758 name and special rules may be applied based on what "get_info" returns
3759 for SQL_CATALOG_NAME_SEPARATOR (41) and SQL_CATALOG_LOCATION (114).
3760 For example, for Oracle:
3761 $id = $dbh->quote_identifier( 'link', 'schema', 'table' );
3763 would return "schema"."table"@"link".
3765 "take_imp_data"
3767 $imp_data = $dbh->take_imp_data;
3769 Leaves the $dbh in an almost dead, zombie-like, state and returns a
3771 binary string of raw implementation data from the driver which
3772 describes the current database connection. Effectively it detaches the
3773 underlying database API connection data from the DBI handle. After
3774 calling take_imp_data(), all other methods except "DESTROY" will
3775 generate a warning and return undef.
3776 Why would you want to do this? You don't, forget I even mentioned it.
3778 Unless, that is, you're implementing something advanced like a multi-
3779 threaded connection pool. See DBI::Pool.
3780 The returned $imp_data can be passed as a "dbi_imp_data" attribute to a
3782 later connect() call, even in a separate thread in the same process,
3783 where the driver can use it to 'adopt' the existing connection that the
3784 implementation data was taken from.
3785 Some things to keep in mind...
3787 * the $imp_data holds the only reference to the underlying database API
3789 connection data. That connection is still 'live' and won't be cleaned
3790 up properly unless the $imp_data is used to create a new $dbh which is
3791 then allowed to disconnect() normally.
3792 * using the same $imp_data to create more than one other new $dbh at a
3794 time may well lead to unpleasant problems. Don't do that.
3795 Any child statement handles are effectively destroyed when
3797 take_imp_data() is called.
3798 The "take_imp_data" method was added in DBI 1.36 but wasn't useful till
3800 1.49.
3801 Database Handle Attributes
3803 This section describes attributes specific to database handles.
3804 Changes to these database handle attributes do not affect any other
3806 existing or future database handles.
3807 Attempting to set or get the value of an unknown attribute generates a
3809 warning, except for private driver-specific attributes (which all have
3810 names starting with a lowercase letter).
3811 Example:
3813 $h->{AutoCommit} = ...; # set/write
3815 ... = $h->{AutoCommit}; # get/read
3816 "AutoCommit"
3818 Type: boolean
3820 If true, then database changes cannot be rolled-back (undone). If
3822 false, then database changes automatically occur within a
3823 "transaction", which must either be committed or rolled back using the
3824 "commit" or "rollback" methods.
3825 Drivers should always default to "AutoCommit" mode (an unfortunate
3827 choice largely forced on the DBI by ODBC and JDBC conventions.)
3828 Attempting to set "AutoCommit" to an unsupported value is a fatal
3830 error. This is an important feature of the DBI. Applications that need
3831 full transaction behaviour can set "$dbh->{AutoCommit} = 0" (or set
3832 "AutoCommit" to 0 via "connect") without having to check that the value
3833 was assigned successfully.
3834 For the purposes of this description, we can divide databases into
3836 three categories:
3837 Databases which don't support transactions at all.
3839 Databases in which a transaction is always active.
3840 Databases in which a transaction must be explicitly started (C<'BEGIN WORK'>).
3841 * Databases which don't support transactions at all
3843 For these databases, attempting to turn "AutoCommit" off is a fatal
3845 error. "commit" and "rollback" both issue warnings about being
3846 ineffective while "AutoCommit" is in effect.
3847 * Databases in which a transaction is always active
3849 These are typically mainstream commercial relational databases with
3851 "ANSI standard" transaction behaviour. If "AutoCommit" is off, then
3852 changes to the database won't have any lasting effect unless "commit"
3853 is called (but see also "disconnect"). If "rollback" is called then any
3854 changes since the last commit are undone.
3855 If "AutoCommit" is on, then the effect is the same as if the DBI called
3857 "commit" automatically after every successful database operation. So
3858 calling "commit" or "rollback" explicitly while "AutoCommit" is on
3859 would be ineffective because the changes would have already been
3860 committed.
3861 Changing "AutoCommit" from off to on will trigger a "commit".
3863 For databases which don't support a specific auto-commit mode, the
3865 driver has to commit each statement automatically using an explicit
3866 "COMMIT" after it completes successfully (and roll it back using an
3867 explicit "ROLLBACK" if it fails). The error information reported to
3868 the application will correspond to the statement which was executed,
3869 unless it succeeded and the commit or rollback failed.
3870 * Databases in which a transaction must be explicitly started
3872 For these databases, the intention is to have them act like databases
3874 in which a transaction is always active (as described above).
3875 To do this, the driver will automatically begin an explicit transaction
3877 when "AutoCommit" is turned off, or after a "commit" or "rollback" (or
3878 when the application issues the next database operation after one of
3879 those events).
3880 In this way, the application does not have to treat these databases as
3882 a special case.
3883 See "commit", "disconnect" and "Transactions" for other important notes
3885 about transactions.
3886 "Driver"
3888 Type: handle
3890 Holds the handle of the parent driver. The only recommended use for
3892 this is to find the name of the driver using:
3893 $dbh->{Driver}->{Name}
3895 "Name"
3897 Type: string
3899 Holds the "name" of the database. Usually (and recommended to be) the
3901 same as the ""dbi:DriverName:..."" string used to connect to the
3902 database, but with the leading ""dbi:DriverName:"" removed.
3903 "Statement"
3905 Type: string, read-only
3907 Returns the statement string passed to the most recent "prepare" or
3909 "do" method called in this database handle, even if that method failed.
3910 This is especially useful where "RaiseError" is enabled and the
3911 exception handler checks $@ and sees that a 'prepare' method call
3912 failed.
3913 "RowCacheSize"
3915 Type: integer
3917 A hint to the driver indicating the size of the local row cache that
3919 the application would like the driver to use for future "SELECT"
3920 statements. If a row cache is not implemented, then setting
3921 "RowCacheSize" is ignored and getting the value returns "undef".
3922 Some "RowCacheSize" values have special meaning, as follows:
3924 0 - Automatically determine a reasonable cache size for each C<SELECT>
3926 1 - Disable the local row cache
3927 >1 - Cache this many rows
3928 <0 - Cache as many rows that will fit into this much memory for each C<SELECT>.
3929 Note that large cache sizes may require a very large amount of memory
3931 (cached rows * maximum size of row). Also, a large cache will cause a
3932 longer delay not only for the first fetch, but also whenever the cache
3933 needs refilling.
3934 See also the "RowsInCache" statement handle attribute.
3936 "Username"
3938 Type: string
3940 Returns the username used to connect to the database.
3942
3944 This section lists the methods and attributes associated with DBI
3945 statement handles.
3946 Statement Handle Methods
3948 The DBI defines the following methods for use on DBI statement handles:
3949 "bind_param"
3951 $sth->bind_param($p_num, $bind_value)
3953 $sth->bind_param($p_num, $bind_value, \%attr)
3954 $sth->bind_param($p_num, $bind_value, $bind_type)
3955 The "bind_param" method takes a copy of $bind_value and associates it
3957 (binds it) with a placeholder, identified by $p_num, embedded in the
3958 prepared statement. Placeholders are indicated with question mark
3959 character ("?"). For example:
3960 $dbh->{RaiseError} = 1; # save having to check each method call
3962 $sth = $dbh->prepare("SELECT name, age FROM people WHERE name LIKE ?");
3963 $sth->bind_param(1, "John%"); # placeholders are numbered from 1
3964 $sth->execute;
3965 DBI::dump_results($sth);
3966 See "Placeholders and Bind Values" for more information.
3968 Data Types for Placeholders
3970 The "\%attr" parameter can be used to hint at the data type the
3972 placeholder should have. This is rarely needed. Typically, the driver
3973 is only interested in knowing if the placeholder should be bound as a
3974 number or a string.
3975 $sth->bind_param(1, $value, { TYPE => SQL_INTEGER });
3977 As a short-cut for the common case, the data type can be passed
3979 directly, in place of the "\%attr" hash reference. This example is
3980 equivalent to the one above:
3981 $sth->bind_param(1, $value, SQL_INTEGER);
3983 The "TYPE" value indicates the standard (non-driver-specific) type for
3985 this parameter. To specify the driver-specific type, the driver may
3986 support a driver-specific attribute, such as "{ ora_type => 97 }".
3987 The SQL_INTEGER and other related constants can be imported using
3989 use DBI qw(:sql_types);
3991 See "DBI Constants" for more information.
3993 The data type is 'sticky' in that bind values passed to execute() are
3995 bound with the data type specified by earlier bind_param() calls, if
3996 any. Portable applications should not rely on being able to change the
3997 data type after the first "bind_param" call.
3998 Perl only has string and number scalar data types. All database types
4000 that aren't numbers are bound as strings and must be in a format the
4001 database will understand except where the bind_param() TYPE attribute
4002 specifies a type that implies a particular format. For example, given:
4003 $sth->bind_param(1, $value, SQL_DATETIME);
4005 the driver should expect $value to be in the ODBC standard SQL_DATETIME
4007 format, which is 'YYYY-MM-DD HH:MM:SS'. Similarly for SQL_DATE,
4008 SQL_TIME etc.
4009 As an alternative to specifying the data type in the "bind_param" call,
4011 you can let the driver pass the value as the default type ("VARCHAR").
4012 You can then use an SQL function to convert the type within the
4013 statement. For example:
4014 INSERT INTO price(code, price) VALUES (?, CONVERT(MONEY,?))
4016 The "CONVERT" function used here is just an example. The actual
4018 function and syntax will vary between different databases and is non-
4019 portable.
4020 See also "Placeholders and Bind Values" for more information.
4022 "bind_param_inout"
4024 $rc = $sth->bind_param_inout($p_num, \$bind_value, $max_len) or die $sth->errstr;
4026 $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, \%attr) or ...
4027 $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, $bind_type) or ...
4028 This method acts like "bind_param", but also enables values to be
4030 updated by the statement. The statement is typically a call to a stored
4031 procedure. The $bind_value must be passed as a reference to the actual
4032 value to be used.
4033 Note that unlike "bind_param", the $bind_value variable is not copied
4035 when "bind_param_inout" is called. Instead, the value in the variable
4036 is read at the time "execute" is called.
4037 The additional $max_len parameter specifies the minimum amount of
4039 memory to allocate to $bind_value for the new value. If the value
4040 returned from the database is too big to fit, then the execution should
4041 fail. If unsure what value to use, pick a generous length, i.e., a
4042 length larger than the longest value that would ever be returned. The
4043 only cost of using a larger value than needed is wasted memory.
4044 Undefined values or "undef" are used to indicate null values. See also
4046 "Placeholders and Bind Values" for more information.
4047 "bind_param_array"
4049 $rc = $sth->bind_param_array($p_num, $array_ref_or_value)
4051 $rc = $sth->bind_param_array($p_num, $array_ref_or_value, \%attr)
4052 $rc = $sth->bind_param_array($p_num, $array_ref_or_value, $bind_type)
4053 The "bind_param_array" method is used to bind an array of values to a
4055 placeholder embedded in the prepared statement which is to be executed
4056 with "execute_array". For example:
4057 $dbh->{RaiseError} = 1; # save having to check each method call
4059 $sth = $dbh->prepare("INSERT INTO staff (first_name, last_name, dept) VALUES(?, ?, ?)");
4060 $sth->bind_param_array(1, [ 'John', 'Mary', 'Tim' ]);
4061 $sth->bind_param_array(2, [ 'Booth', 'Todd', 'Robinson' ]);
4062 $sth->bind_param_array(3, "SALES"); # scalar will be reused for each row
4063 $sth->execute_array( { ArrayTupleStatus => \my @tuple_status } );
4064 The %attr ($bind_type) argument is the same as defined for
4066 "bind_param". Refer to "bind_param" for general details on using
4067 placeholders.
4068 (Note that bind_param_array() can not be used to expand a placeholder
4070 into a list of values for a statement like "SELECT foo WHERE bar IN
4071 (?)". A placeholder can only ever represent one value per execution.)
4072 Scalar values, including "undef", may also be bound by
4074 "bind_param_array". In which case the same value will be used for each
4075 "execute" call. Driver-specific implementations may behave differently,
4076 e.g., when binding to a stored procedure call, some databases may
4077 permit mixing scalars and arrays as arguments.
4078 The default implementation provided by DBI (for drivers that have not
4080 implemented array binding) is to iteratively call "execute" for each
4081 parameter tuple provided in the bound arrays. Drivers may provide more
4082 optimized implementations using whatever bulk operation support the
4083 database API provides. The default driver behaviour should match the
4084 default DBI behaviour, but always consult your driver documentation as
4085 there may be driver specific issues to consider.
4086 Note that the default implementation currently only supports non-data
4088 returning statements (INSERT, UPDATE, but not SELECT). Also,
4089 "bind_param_array" and "bind_param" cannot be mixed in the same
4090 statement execution, and "bind_param_array" must be used with
4091 "execute_array"; using "bind_param_array" will have no effect for
4092 "execute".
4093 The "bind_param_array" method was added in DBI 1.22.
4095 "execute"
4097 $rv = $sth->execute or die $sth->errstr;
4099 $rv = $sth->execute(@bind_values) or die $sth->errstr;
4100 Perform whatever processing is necessary to execute the prepared
4102 statement. An "undef" is returned if an error occurs. A successful
4103 "execute" always returns true regardless of the number of rows
4104 affected, even if it's zero (see below). It is always important to
4105 check the return status of "execute" (and most other DBI methods) for
4106 errors if you're not using "RaiseError".
4107 For a non-"SELECT" statement, "execute" returns the number of rows
4109 affected, if known. If no rows were affected, then "execute" returns
4110 "0E0", which Perl will treat as 0 but will regard as true. Note that it
4111 is not an error for no rows to be affected by a statement. If the
4112 number of rows affected is not known, then "execute" returns -1.
4113 For "SELECT" statements, execute simply "starts" the query within the
4115 database engine. Use one of the fetch methods to retrieve the data
4116 after calling "execute". The "execute" method does not return the
4117 number of rows that will be returned by the query (because most
4118 databases can't tell in advance), it simply returns a true value.
4119 You can tell if the statement was a "SELECT" statement by checking if
4121 "$sth->{NUM_OF_FIELDS}" is greater than zero after calling "execute".
4122 If any arguments are given, then "execute" will effectively call
4124 "bind_param" for each value before executing the statement. Values
4125 bound in this way are usually treated as "SQL_VARCHAR" types unless the
4126 driver can determine the correct type (which is rare), or unless
4127 "bind_param" (or "bind_param_inout") has already been used to specify
4128 the type.
4129 Note that passing "execute" an empty array is the same as passing no
4131 arguments at all, which will execute the statement with previously
4132 bound values. That's probably not what you want.
4133 If execute() is called on a statement handle that's still active
4135 ($sth->{Active} is true) then it should effectively call finish() to
4136 tidy up the previous execution results before starting this new
4137 execution.
4138 "execute_array"
4140 $tuples = $sth->execute_array(\%attr) or die $sth->errstr;
4142 $tuples = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
4143 ($tuples, $rows) = $sth->execute_array(\%attr) or die $sth->errstr;
4145 ($tuples, $rows) = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
4146 Execute the prepared statement once for each parameter tuple (group of
4148 values) provided either in the @bind_values, or by prior calls to
4149 "bind_param_array", or via a reference passed in \%attr.
4150 When called in scalar context the execute_array() method returns the
4152 number of tuples executed, or "undef" if an error occurred. Like
4153 execute(), a successful execute_array() always returns true regardless
4154 of the number of tuples executed, even if it's zero. If there were any
4155 errors the ArrayTupleStatus array can be used to discover which tuples
4156 failed and with what errors.
4157 When called in list context the execute_array() method returns two
4159 scalars; $tuples is the same as calling execute_array() in scalar
4160 context and $rows is the number of rows affected for each tuple, if
4161 available or -1 if the driver cannot determine this. NOTE, some drivers
4162 cannot determine the number of rows affected per tuple but can provide
4163 the number of rows affected for the batch. If you are doing an update
4164 operation the returned rows affected may not be what you expect if, for
4165 instance, one or more of the tuples affected the same row multiple
4166 times. Some drivers may not yet support list context, in which case
4167 $rows will be undef, or may not be able to provide the number of rows
4168 affected when performing this batch operation, in which case $rows will
4169 be -1.
4170 Bind values for the tuples to be executed may be supplied row-wise by
4172 an "ArrayTupleFetch" attribute, or else column-wise in the @bind_values
4173 argument, or else column-wise by prior calls to "bind_param_array".
4174 Where column-wise binding is used (via the @bind_values argument or
4176 calls to bind_param_array()) the maximum number of elements in any one
4177 of the bound value arrays determines the number of tuples executed.
4178 Placeholders with fewer values in their parameter arrays are treated as
4179 if padded with undef (NULL) values.
4180 If a scalar value is bound, instead of an array reference, it is
4182 treated as a variable length array with all elements having the same
4183 value. It does not influence the number of tuples executed, so if all
4184 bound arrays have zero elements then zero tuples will be executed. If
4185 all bound values are scalars then one tuple will be executed, making
4186 execute_array() act just like execute().
4187 The "ArrayTupleFetch" attribute can be used to specify a reference to a
4189 subroutine that will be called to provide the bind values for each
4190 tuple execution. The subroutine should return an reference to an array
4191 which contains the appropriate number of bind values, or return an
4192 undef if there is no more data to execute.
4193 As a convenience, the "ArrayTupleFetch" attribute can also be used to
4195 specify a statement handle. In which case the fetchrow_arrayref()
4196 method will be called on the given statement handle in order to provide
4197 the bind values for each tuple execution.
4198 The values specified via bind_param_array() or the @bind_values
4200 parameter may be either scalars, or arrayrefs. If any @bind_values are
4201 given, then "execute_array" will effectively call "bind_param_array"
4202 for each value before executing the statement. Values bound in this
4203 way are usually treated as "SQL_VARCHAR" types unless the driver can
4204 determine the correct type (which is rare), or unless "bind_param",
4205 "bind_param_inout", "bind_param_array", or "bind_param_inout_array" has
4206 already been used to specify the type. See "bind_param_array" for
4207 details.
4208 The "ArrayTupleStatus" attribute can be used to specify a reference to
4210 an array which will receive the execute status of each executed
4211 parameter tuple. Note the "ArrayTupleStatus" attribute was mandatory
4212 until DBI 1.38.
4213 For tuples which are successfully executed, the element at the same
4215 ordinal position in the status array is the resulting rowcount (or -1
4216 if unknown). If the execution of a tuple causes an error, then the
4217 corresponding status array element will be set to a reference to an
4218 array containing "err", "errstr" and "state" set by the failed
4219 execution.
4220 If any tuple execution returns an error, "execute_array" will return
4222 "undef". In that case, the application should inspect the status array
4223 to determine which parameter tuples failed. Some databases may not
4224 continue executing tuples beyond the first failure. In this case the
4225 status array will either hold fewer elements, or the elements beyond
4226 the failure will be undef.
4227 If all parameter tuples are successfully executed, "execute_array"
4229 returns the number tuples executed. If no tuples were executed, then
4230 execute_array() returns "0E0", just like execute() does, which Perl
4231 will treat as 0 but will regard as true.
4232 For example:
4234 $sth = $dbh->prepare("INSERT INTO staff (first_name, last_name) VALUES (?, ?)");
4236 my $tuples = $sth->execute_array(
4237 { ArrayTupleStatus => \my @tuple_status },
4238 \@first_names,
4239 \@last_names,
4240 );
4241 if ($tuples) {
4242 print "Successfully inserted $tuples records\n";
4243 }
4244 else {
4245 for my $tuple (0..@last_names-1) {
4246 my $status = $tuple_status[$tuple];
4247 $status = [0, "Skipped"] unless defined $status;
4248 next unless ref $status;
4249 printf "Failed to insert (%s, %s): %s\n",
4250 $first_names[$tuple], $last_names[$tuple], $status->[1];
4251 }
4252 }
4253 Support for data returning statements such as SELECT is driver-specific
4255 and subject to change. At present, the default implementation provided
4256 by DBI only supports non-data returning statements.
4257 Transaction semantics when using array binding are driver and database
4259 specific. If "AutoCommit" is on, the default DBI implementation will
4260 cause each parameter tuple to be individually committed (or rolled back
4261 in the event of an error). If "AutoCommit" is off, the application is
4262 responsible for explicitly committing the entire set of bound parameter
4263 tuples. Note that different drivers and databases may have different
4264 behaviours when some parameter tuples cause failures. In some cases,
4265 the driver or database may automatically rollback the effect of all
4266 prior parameter tuples that succeeded in the transaction; other drivers
4267 or databases may retain the effect of prior successfully executed
4268 parameter tuples. Be sure to check your driver and database for its
4269 specific behaviour.
4270 Note that, in general, performance will usually be better with
4272 "AutoCommit" turned off, and using explicit "commit" after each
4273 "execute_array" call.
4274 The "execute_array" method was added in DBI 1.22, and ArrayTupleFetch
4276 was added in 1.36.
4277 "execute_for_fetch"
4279 $tuples = $sth->execute_for_fetch($fetch_tuple_sub);
4281 $tuples = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
4282 ($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub);
4284 ($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
4285 The execute_for_fetch() method is used to perform bulk operations and
4287 although it is most often used via the execute_array() method you can
4288 use it directly. The main difference between execute_array and
4289 execute_for_fetch is the former does column or row-wise binding and the
4290 latter uses row-wise binding.
4291 The fetch subroutine, referenced by $fetch_tuple_sub, is expected to
4293 return a reference to an array (known as a 'tuple') or undef.
4294 The execute_for_fetch() method calls $fetch_tuple_sub, without any
4296 parameters, until it returns a false value. Each tuple returned is used
4297 to provide bind values for an $sth->execute(@$tuple) call.
4298 In scalar context execute_for_fetch() returns "undef" if there were any
4300 errors and the number of tuples executed otherwise. Like execute() and
4301 execute_array() a zero is returned as "0E0" so execute_for_fetch() is
4302 only false on error. If there were any errors the @tuple_status array
4303 can be used to discover which tuples failed and with what errors.
4304 When called in list context execute_for_fetch() returns two scalars;
4306 $tuples is the same as calling execute_for_fetch() in scalar context
4307 and $rows is the sum of the number of rows affected for each tuple, if
4308 available or -1 if the driver cannot determine this. If you are doing
4309 an update operation the returned rows affected may not be what you
4310 expect if, for instance, one or more of the tuples affected the same
4311 row multiple times. Some drivers may not yet support list context, in
4312 which case $rows will be undef, or may not be able to provide the
4313 number of rows affected when performing this batch operation, in which
4314 case $rows will be -1.
4315 If \@tuple_status is passed then the execute_for_fetch method uses it
4317 to return status information. The tuple_status array holds one element
4318 per tuple. If the corresponding execute() did not fail then the element
4319 holds the return value from execute(), which is typically a row count.
4320 If the execute() did fail then the element holds a reference to an
4321 array containing ($sth->err, $sth->errstr, $sth->state).
4322 If the driver detects an error that it knows means no further tuples
4324 can be executed then it may return, with an error status, even though
4325 $fetch_tuple_sub may still have more tuples to be executed.
4326 Although each tuple returned by $fetch_tuple_sub is effectively used to
4328 call $sth->execute(@$tuple_array_ref) the exact timing may vary.
4329 Drivers are free to accumulate sets of tuples to pass to the database
4330 server in bulk group operations for more efficient execution. However,
4331 the $fetch_tuple_sub is specifically allowed to return the same array
4332 reference each time (which is what fetchrow_arrayref() usually does).
4333 For example:
4335 my $sel = $dbh1->prepare("select foo, bar from table1");
4337 $sel->execute;
4338 my $ins = $dbh2->prepare("insert into table2 (foo, bar) values (?,?)");
4340 my $fetch_tuple_sub = sub { $sel->fetchrow_arrayref };
4341 my @tuple_status;
4343 $rc = $ins->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
4344 my @errors = grep { ref $_ } @tuple_status;
4345 Similarly, if you already have an array containing the data rows to be
4347 processed you'd use a subroutine to shift off and return each array ref
4348 in turn:
4349 $ins->execute_for_fetch( sub { shift @array_of_arrays }, \@tuple_status);
4351 The "execute_for_fetch" method was added in DBI 1.38.
4353 "fetchrow_arrayref"
4355 $ary_ref = $sth->fetchrow_arrayref;
4357 $ary_ref = $sth->fetch; # alias
4358 Fetches the next row of data and returns a reference to an array
4360 holding the field values. Null fields are returned as "undef" values
4361 in the array. This is the fastest way to fetch data, particularly if
4362 used with "$sth->bind_columns".
4363 If there are no more rows or if an error occurs, then
4365 "fetchrow_arrayref" returns an "undef". You should check "$sth->err"
4366 afterwards (or use the "RaiseError" attribute) to discover if the
4367 "undef" returned was due to an error.
4368 Note that the same array reference is returned for each fetch, so don't
4370 store the reference and then use it after a later fetch. Also, the
4371 elements of the array are also reused for each row, so take care if you
4372 want to take a reference to an element. See also "bind_columns".
4373 "fetchrow_array"
4375 @ary = $sth->fetchrow_array;
4377 An alternative to "fetchrow_arrayref". Fetches the next row of data and
4379 returns it as a list containing the field values. Null fields are
4380 returned as "undef" values in the list.
4381 If there are no more rows or if an error occurs, then "fetchrow_array"
4383 returns an empty list. You should check "$sth->err" afterwards (or use
4384 the "RaiseError" attribute) to discover if the empty list returned was
4385 due to an error.
4386 If called in a scalar context for a statement handle that has more than
4388 one column, it is undefined whether the driver will return the value of
4389 the first column or the last. So don't do that. Also, in a scalar
4390 context, an "undef" is returned if there are no more rows or if an
4391 error occurred. That "undef" can't be distinguished from an "undef"
4392 returned because the first field value was NULL. For these reasons you
4393 should exercise some caution if you use "fetchrow_array" in a scalar
4394 context.
4395 "fetchrow_hashref"
4397 $hash_ref = $sth->fetchrow_hashref;
4399 $hash_ref = $sth->fetchrow_hashref($name);
4400 An alternative to "fetchrow_arrayref". Fetches the next row of data and
4402 returns it as a reference to a hash containing field name and field
4403 value pairs. Null fields are returned as "undef" values in the hash.
4404 If there are no more rows or if an error occurs, then
4406 "fetchrow_hashref" returns an "undef". You should check "$sth->err"
4407 afterwards (or use the "RaiseError" attribute) to discover if the
4408 "undef" returned was due to an error.
4409 The optional $name parameter specifies the name of the statement handle
4411 attribute. For historical reasons it defaults to ""NAME"", however
4412 using either ""NAME_lc"" or ""NAME_uc"" is recommended for portability.
4413 The keys of the hash are the same names returned by "$sth->{$name}". If
4415 more than one field has the same name, there will only be one entry in
4416 the returned hash for those fields, so statements like ""select foo,
4417 foo from bar"" will return only a single key from "fetchrow_hashref".
4418 In these cases use column aliases or "fetchrow_arrayref". Note that it
4419 is the database server (and not the DBD implementation) which provides
4420 the name for fields containing functions like "count(*)" or
4421 ""max(c_foo)"" and they may clash with existing column names (most
4422 databases don't care about duplicate column names in a result-set). If
4423 you want these to return as unique names that are the same across
4424 databases, use aliases, as in ""select count(*) as cnt"" or ""select
4425 max(c_foo) mx_foo, ..."" depending on the syntax your database
4426 supports.
4427 Because of the extra work "fetchrow_hashref" and Perl have to perform,
4429 it is not as efficient as "fetchrow_arrayref" or "fetchrow_array".
4430 By default a reference to a new hash is returned for each row. It is
4432 likely that a future version of the DBI will support an attribute which
4433 will enable the same hash to be reused for each row. This will give a
4434 significant performance boost, but it won't be enabled by default
4435 because of the risk of breaking old code.
4436 "fetchall_arrayref"
4438 $tbl_ary_ref = $sth->fetchall_arrayref;
4440 $tbl_ary_ref = $sth->fetchall_arrayref( $slice );
4441 $tbl_ary_ref = $sth->fetchall_arrayref( $slice, $max_rows );
4442 The "fetchall_arrayref" method can be used to fetch all the data to be
4444 returned from a prepared and executed statement handle. It returns a
4445 reference to an array that contains one reference per row.
4446 If called on an inactive statement handle, "fetchall_arrayref" returns
4448 undef.
4449 If there are no rows left to return from an active statement handle,
4451 "fetchall_arrayref" returns a reference to an empty array. If an error
4452 occurs, "fetchall_arrayref" returns the data fetched thus far, which
4453 may be none. You should check "$sth->err" afterwards (or use the
4454 "RaiseError" attribute) to discover if the data is complete or was
4455 truncated due to an error.
4456 If $slice is an array reference, "fetchall_arrayref" uses
4458 "fetchrow_arrayref" to fetch each row as an array ref. If the $slice
4459 array is not empty then it is used as a slice to select individual
4460 columns by perl array index number (starting at 0, unlike column and
4461 parameter numbers which start at 1).
4462 With no parameters, or if $slice is undefined, "fetchall_arrayref" acts
4464 as if passed an empty array ref.
4465 For example, to fetch just the first column of every row:
4467 $tbl_ary_ref = $sth->fetchall_arrayref([0]);
4469 To fetch the second to last and last column of every row:
4471 $tbl_ary_ref = $sth->fetchall_arrayref([-2,-1]);
4473 Those two examples both return a reference to an array of array refs.
4475 If $slice is a hash reference, "fetchall_arrayref" fetches each row as
4477 a hash reference. If the $slice hash is empty then the keys in the
4478 hashes have whatever name lettercase is returned by default. (See
4479 "FetchHashKeyName" attribute.) If the $slice hash is not empty, then it
4480 is used as a slice to select individual columns by name. The values of
4481 the hash should be set to 1. The key names of the returned hashes
4482 match the letter case of the names in the parameter hash, regardless of
4483 the "FetchHashKeyName" attribute.
4484 For example, to fetch all fields of every row as a hash ref:
4486 $tbl_ary_ref = $sth->fetchall_arrayref({});
4488 To fetch only the fields called "foo" and "bar" of every row as a hash
4490 ref (with keys named "foo" and "BAR", regardless of the original
4491 capitalization):
4492 $tbl_ary_ref = $sth->fetchall_arrayref({ foo=>1, BAR=>1 });
4494 Those two examples both return a reference to an array of hash refs.
4496 If $slice is a reference to a hash reference, that hash is used to
4498 select and rename columns. The keys are 0-based column index numbers
4499 and the values are the corresponding keys for the returned row hashes.
4500 For example, to fetch only the first and second columns of every row as
4502 a hash ref (with keys named "k" and "v" regardless of their original
4503 names):
4504 $tbl_ary_ref = $sth->fetchall_arrayref( \{ 0 => 'k', 1 => 'v' } );
4506 If $max_rows is defined and greater than or equal to zero then it is
4508 used to limit the number of rows fetched before returning.
4509 fetchall_arrayref() can then be called again to fetch more rows. This
4510 is especially useful when you need the better performance of
4511 fetchall_arrayref() but don't have enough memory to fetch and return
4512 all the rows in one go.
4513 Here's an example (assumes RaiseError is enabled):
4515 my $rows = []; # cache for batches of rows
4517 while( my $row = ( shift(@$rows) || # get row from cache, or reload cache:
4518 shift(@{$rows=$sth->fetchall_arrayref(undef,10_000)||[]}) )
4519 ) {
4520 ...
4521 }
4522 That might be the fastest way to fetch and process lots of rows using
4524 the DBI, but it depends on the relative cost of method calls vs memory
4525 allocation.
4526 A standard "while" loop with column binding is often faster because the
4528 cost of allocating memory for the batch of rows is greater than the
4529 saving by reducing method calls. It's possible that the DBI may provide
4530 a way to reuse the memory of a previous batch in future, which would
4531 then shift the balance back towards fetchall_arrayref().
4532 "fetchall_hashref"
4534 $hash_ref = $sth->fetchall_hashref($key_field);
4536 The "fetchall_hashref" method can be used to fetch all the data to be
4538 returned from a prepared and executed statement handle. It returns a
4539 reference to a hash containing a key for each distinct value of the
4540 $key_field column that was fetched. For each key the corresponding
4541 value is a reference to a hash containing all the selected columns and
4542 their values, as returned by "fetchrow_hashref()".
4543 If there are no rows to return, "fetchall_hashref" returns a reference
4545 to an empty hash. If an error occurs, "fetchall_hashref" returns the
4546 data fetched thus far, which may be none. You should check "$sth->err"
4547 afterwards (or use the "RaiseError" attribute) to discover if the data
4548 is complete or was truncated due to an error.
4549 The $key_field parameter provides the name of the field that holds the
4551 value to be used for the key for the returned hash. For example:
4552 $dbh->{FetchHashKeyName} = 'NAME_lc';
4554 $sth = $dbh->prepare("SELECT FOO, BAR, ID, NAME, BAZ FROM TABLE");
4555 $sth->execute;
4556 $hash_ref = $sth->fetchall_hashref('id');
4557 print "Name for id 42 is $hash_ref->{42}->{name}\n";
4558 The $key_field parameter can also be specified as an integer column
4560 number (counting from 1). If $key_field doesn't match any column in
4561 the statement, as a name first then as a number, then an error is
4562 returned.
4563 For queries returning more than one 'key' column, you can specify
4565 multiple column names by passing $key_field as a reference to an array
4566 containing one or more key column names (or index numbers). For
4567 example:
4568 $sth = $dbh->prepare("SELECT foo, bar, baz FROM table");
4570 $sth->execute;
4571 $hash_ref = $sth->fetchall_hashref( [ qw(foo bar) ] );
4572 print "For foo 42 and bar 38, baz is $hash_ref->{42}->{38}->{baz}\n";
4573 The fetchall_hashref() method is normally used only where the key
4575 fields values for each row are unique. If multiple rows are returned
4576 with the same values for the key fields then later rows overwrite
4577 earlier ones.
4578 "finish"
4580 $rc = $sth->finish;
4582 Indicate that no more data will be fetched from this statement handle
4584 before it is either executed again or destroyed. You almost certainly
4585 do not need to call this method.
4586 Adding calls to "finish" after loop that fetches all rows is a common
4588 mistake, don't do it, it can mask genuine problems like uncaught fetch
4589 errors.
4590 When all the data has been fetched from a "SELECT" statement, the
4592 driver will automatically call "finish" for you. So you should not call
4593 it explicitly except when you know that you've not fetched all the data
4594 from a statement handle and the handle won't be destroyed soon.
4595 The most common example is when you only want to fetch just one row,
4597 but in that case the "selectrow_*" methods are usually better anyway.
4598 Consider a query like:
4600 SELECT foo FROM table WHERE bar=? ORDER BY baz
4602 on a very large table. When executed, the database server will have to
4604 use temporary buffer space to store the sorted rows. If, after
4605 executing the handle and selecting just a few rows, the handle won't be
4606 re-executed for some time and won't be destroyed, the "finish" method
4607 can be used to tell the server that the buffer space can be freed.
4608 Calling "finish" resets the "Active" attribute for the statement. It
4610 may also make some statement handle attributes (such as "NAME" and
4611 "TYPE") unavailable if they have not already been accessed (and thus
4612 cached).
4613 The "finish" method does not affect the transaction status of the
4615 database connection. It has nothing to do with transactions. It's
4616 mostly an internal "housekeeping" method that is rarely needed. See
4617 also "disconnect" and the "Active" attribute.
4618 The "finish" method should have been called "discard_pending_rows".
4620 "rows"
4622 $rv = $sth->rows;
4624 Returns the number of rows affected by the last row affecting command,
4626 or -1 if the number of rows is not known or not available.
4627 Generally, you can only rely on a row count after a non-"SELECT"
4629 "execute" (for some specific operations like "UPDATE" and "DELETE"), or
4630 after fetching all the rows of a "SELECT" statement.
4631 For "SELECT" statements, it is generally not possible to know how many
4633 rows will be returned except by fetching them all. Some drivers will
4634 return the number of rows the application has fetched so far, but
4635 others may return -1 until all rows have been fetched. So use of the
4636 "rows" method or $DBI::rows with "SELECT" statements is not
4637 recommended.
4638 One alternative method to get a row count for a "SELECT" is to execute
4640 a "SELECT COUNT(*) FROM ..." SQL statement with the same "..." as your
4641 query and then fetch the row count from that.
4642 "bind_col"
4644 $rc = $sth->bind_col($column_number, \$var_to_bind);
4646 $rc = $sth->bind_col($column_number, \$var_to_bind, \%attr );
4647 $rc = $sth->bind_col($column_number, \$var_to_bind, $bind_type );
4648 Binds a Perl variable and/or some attributes to an output column
4650 (field) of a "SELECT" statement. Column numbers count up from 1. You
4651 do not need to bind output columns in order to fetch data. For maximum
4652 portability between drivers, bind_col() should be called after
4653 execute() and not before. See also "bind_columns" for an example.
4654 The binding is performed at a low level using Perl aliasing. Whenever
4656 a row is fetched from the database $var_to_bind appears to be
4657 automatically updated simply because it now refers to the same memory
4658 location as the corresponding column value. This makes using bound
4659 variables very efficient. Binding a tied variable doesn't work,
4660 currently.
4661 The "bind_param" method performs a similar, but opposite, function for
4663 input variables.
4664 Data Types for Column Binding
4666 The "\%attr" parameter can be used to hint at the data type formatting
4668 the column should have. For example, you can use:
4669 $sth->bind_col(1, undef, { TYPE => SQL_DATETIME });
4671 to specify that you'd like the column (which presumably is some kind of
4673 datetime type) to be returned in the standard format for SQL_DATETIME,
4674 which is 'YYYY-MM-DD HH:MM:SS', rather than the native formatting the
4675 database would normally use.
4676 There's no $var_to_bind in that example to emphasize the point that
4678 bind_col() works on the underlying column and not just a particular
4679 bound variable.
4680 As a short-cut for the common case, the data type can be passed
4682 directly, in place of the "\%attr" hash reference. This example is
4683 equivalent to the one above:
4684 $sth->bind_col(1, undef, SQL_DATETIME);
4686 The "TYPE" value indicates the standard (non-driver-specific) type for
4688 this parameter. To specify the driver-specific type, the driver may
4689 support a driver-specific attribute, such as "{ ora_type => 97 }".
4690 The SQL_DATETIME and other related constants can be imported using
4692 use DBI qw(:sql_types);
4694 See "DBI Constants" for more information.
4696 Few drivers support specifying a data type via a "bind_col" call (most
4698 will simply ignore the data type). Fewer still allow the data type to
4699 be altered once set. If you do set a column type the type should remain
4700 sticky through further calls to bind_col for the same column if the
4701 type is not overridden (this is important for instance when you are
4702 using a slice in fetchall_arrayref).
4703 The TYPE attribute for bind_col() was first specified in DBI 1.41.
4705 From DBI 1.611, drivers can use the "TYPE" attribute to attempt to cast
4707 the bound scalar to a perl type which more closely matches "TYPE". At
4708 present DBI supports "SQL_INTEGER", "SQL_DOUBLE" and "SQL_NUMERIC". See
4709 "sql_type_cast" for details of how types are cast.
4710 Other attributes for Column Binding
4712 The "\%attr" parameter may also contain the following attributes:
4714 "StrictlyTyped"
4716 If a "TYPE" attribute is passed to bind_col, then the driver will
4717 attempt to change the bound perl scalar to match the type more
4718 closely. If the bound value cannot be cast to the requested "TYPE"
4719 then by default it is left untouched and no error is generated. If
4720 you specify "StrictlyTyped" as 1 and the cast fails, this will
4721 generate an error.
4722 This attribute was first added in DBI 1.611. When 1.611 was
4724 released few drivers actually supported this attribute but
4725 DBD::Oracle and DBD::ODBC should from versions 1.24.
4726 "DiscardString"
4728 When the "TYPE" attribute is passed to "bind_col" and the driver
4729 successfully casts the bound perl scalar to a non-string type then
4730 if "DiscardString" is set to 1, the string portion of the scalar
4731 will be discarded. By default, "DiscardString" is not set.
4732 This attribute was first added in DBI 1.611. When 1.611 was
4734 released few drivers actually supported this attribute but
4735 DBD::Oracle and DBD::ODBC should from versions 1.24.
4736 "bind_columns"
4738 $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
4740 Calls "bind_col" for each column of the "SELECT" statement.
4742 The list of references should have the same number of elements as the
4744 number of columns in the "SELECT" statement. If it doesn't then
4745 "bind_columns" will bind the elements given, up to the number of
4746 columns, and then return an error.
4747 For maximum portability between drivers, bind_columns() should be
4749 called after execute() and not before.
4750 For example:
4752 $dbh->{RaiseError} = 1; # do this, or check every call for errors
4754 $sth = $dbh->prepare(q{ SELECT region, sales FROM sales_by_region });
4755 $sth->execute;
4756 my ($region, $sales);
4757 # Bind Perl variables to columns:
4759 $rv = $sth->bind_columns(\$region, \$sales);
4760 # you can also use Perl's \(...) syntax (see perlref docs):
4762 # $sth->bind_columns(\($region, $sales));
4763 # Column binding is the most efficient way to fetch data
4765 while ($sth->fetch) {
4766 print "$region: $sales\n";
4767 }
4768 For compatibility with old scripts, the first parameter will be ignored
4770 if it is "undef" or a hash reference.
4771 Here's a more fancy example that binds columns to the values inside a
4773 hash (thanks to H.Merijn Brand):
4774 $sth->execute;
4776 my %row;
4777 $sth->bind_columns( \( @row{ @{$sth->{NAME_lc} } } ));
4778 while ($sth->fetch) {
4779 print "$row{region}: $row{sales}\n";
4780 }
4781 "dump_results"
4783 $rows = $sth->dump_results($maxlen, $lsep, $fsep, $fh);
4785 Fetches all the rows from $sth, calls "DBI::neat_list" for each row,
4787 and prints the results to $fh (defaults to "STDOUT") separated by $lsep
4788 (default "\n"). $fsep defaults to ", " and $maxlen defaults to 35.
4789 This method is designed as a handy utility for prototyping and testing
4791 queries. Since it uses "neat_list" to format and edit the string for
4792 reading by humans, it is not recommended for data transfer
4793 applications.
4794 Statement Handle Attributes
4796 This section describes attributes specific to statement handles. Most
4797 of these attributes are read-only.
4798 Changes to these statement handle attributes do not affect any other
4800 existing or future statement handles.
4801 Attempting to set or get the value of an unknown attribute generates a
4803 warning, except for private driver specific attributes (which all have
4804 names starting with a lowercase letter).
4805 Example:
4807 ... = $h->{NUM_OF_FIELDS}; # get/read
4809 Some drivers cannot provide valid values for some or all of these
4811 attributes until after "$sth->execute" has been successfully called.
4812 Typically the attribute will be "undef" in these situations.
4813 Some attributes, like NAME, are not appropriate to some types of
4815 statement, like SELECT. Typically the attribute will be "undef" in
4816 these situations.
4817 For drivers which support stored procedures and multiple result sets
4819 (see "more_results") these attributes relate to the current result set.
4820 See also "finish" to learn more about the effect it may have on some
4822 attributes.
4823 "NUM_OF_FIELDS"
4825 Type: integer, read-only
4827 Number of fields (columns) in the data the prepared statement may
4829 return. Statements that don't return rows of data, like "DELETE" and
4830 "CREATE" set "NUM_OF_FIELDS" to 0 (though it may be undef in some
4831 drivers).
4832 "NUM_OF_PARAMS"
4834 Type: integer, read-only
4836 The number of parameters (placeholders) in the prepared statement. See
4838 SUBSTITUTION VARIABLES below for more details.
4839 "NAME"
4841 Type: array-ref, read-only
4843 Returns a reference to an array of field names for each column. The
4845 names may contain spaces but should not be truncated or have any
4846 trailing space. Note that the names have the letter case (upper, lower
4847 or mixed) as returned by the driver being used. Portable applications
4848 should use "NAME_lc" or "NAME_uc".
4849 print "First column name: $sth->{NAME}->[0]\n";
4851 Also note that the name returned for (aggregate) functions like
4853 count(*) or "max(c_foo)" is determined by the database server and not
4854 by "DBI" or the "DBD" backend.
4855 "NAME_lc"
4857 Type: array-ref, read-only
4859 Like "/NAME" but always returns lowercase names.
4861 "NAME_uc"
4863 Type: array-ref, read-only
4865 Like "/NAME" but always returns uppercase names.
4867 "NAME_hash"
4869 Type: hash-ref, read-only
4871 "NAME_lc_hash"
4873 Type: hash-ref, read-only
4875 "NAME_uc_hash"
4877 Type: hash-ref, read-only
4879 The "NAME_hash", "NAME_lc_hash", and "NAME_uc_hash" attributes return
4881 column name information as a reference to a hash.
4882 The keys of the hash are the names of the columns. The letter case of
4884 the keys corresponds to the letter case returned by the "NAME",
4885 "NAME_lc", and "NAME_uc" attributes respectively (as described above).
4886 The value of each hash entry is the perl index number of the
4888 corresponding column (counting from 0). For example:
4889 $sth = $dbh->prepare("select Id, Name from table");
4891 $sth->execute;
4892 @row = $sth->fetchrow_array;
4893 print "Name $row[ $sth->{NAME_lc_hash}{name} ]\n";
4894 "TYPE"
4896 Type: array-ref, read-only
4898 Returns a reference to an array of integer values for each column. The
4900 value indicates the data type of the corresponding column.
4901 The values correspond to the international standards (ANSI X3.135 and
4903 ISO/IEC 9075) which, in general terms, means ODBC. Driver-specific
4904 types that don't exactly match standard types should generally return
4905 the same values as an ODBC driver supplied by the makers of the
4906 database. That might include private type numbers in ranges the vendor
4907 has officially registered with the ISO working group:
4908 ftp://sqlstandards.org/SC32/SQL_Registry/
4910 Where there's no vendor-supplied ODBC driver to be compatible with, the
4912 DBI driver can use type numbers in the range that is now officially
4913 reserved for use by the DBI: -9999 to -9000.
4914 All possible values for "TYPE" should have at least one entry in the
4916 output of the "type_info_all" method (see "type_info_all").
4917 "PRECISION"
4919 Type: array-ref, read-only
4921 Returns a reference to an array of integer values for each column.
4923 For numeric columns, the value is the maximum number of digits (without
4925 considering a sign character or decimal point). Note that the "display
4926 size" for floating point types (REAL, FLOAT, DOUBLE) can be up to 7
4927 characters greater than the precision (for the sign + decimal point +
4928 the letter E + a sign + 2 or 3 digits).
4929 For any character type column the value is the OCTET_LENGTH, in other
4931 words the number of bytes, not characters.
4932 (More recent standards refer to this as COLUMN_SIZE but we stick with
4934 PRECISION for backwards compatibility.)
4935 "SCALE"
4937 Type: array-ref, read-only
4939 Returns a reference to an array of integer values for each column.
4941 NULL ("undef") values indicate columns where scale is not applicable.
4942 "NULLABLE"
4944 Type: array-ref, read-only
4946 Returns a reference to an array indicating the possibility of each
4948 column returning a null. Possible values are 0 (or an empty string) =
4949 no, 1 = yes, 2 = unknown.
4950 print "First column may return NULL\n" if $sth->{NULLABLE}->[0];
4952 "CursorName"
4954 Type: string, read-only
4956 Returns the name of the cursor associated with the statement handle, if
4958 available. If not available or if the database driver does not support
4959 the "where current of ..." SQL syntax, then it returns "undef".
4960 "Database"
4962 Type: dbh, read-only
4964 Returns the parent $dbh of the statement handle.
4966 "Statement"
4968 Type: string, read-only
4970 Returns the statement string passed to the "prepare" method.
4972 "ParamValues"
4974 Type: hash ref, read-only
4976 Returns a reference to a hash containing the values currently bound to
4978 placeholders. The keys of the hash are the 'names' of the
4979 placeholders, typically integers starting at 1. Returns undef if not
4980 supported by the driver.
4981 See "ShowErrorStatement" for an example of how this is used.
4983 * Keys:
4985 If the driver supports "ParamValues" but no values have been bound yet
4987 then the driver should return a hash with placeholders names in the
4988 keys but all the values undef, but some drivers may return a ref to an
4989 empty hash because they can't pre-determine the names.
4990 It is possible that the keys in the hash returned by "ParamValues" are
4992 not exactly the same as those implied by the prepared statement. For
4993 example, DBD::Oracle translates '"?"' placeholders into '":pN"' where N
4994 is a sequence number starting at 1.
4995 * Values:
4997 It is possible that the values in the hash returned by "ParamValues"
4999 are not exactly the same as those passed to bind_param() or execute().
5000 The driver may have slightly modified values in some way based on the
5001 TYPE the value was bound with. For example a floating point value bound
5002 as an SQL_INTEGER type may be returned as an integer. The values
5003 returned by "ParamValues" can be passed to another bind_param() method
5004 with the same TYPE and will be seen by the database as the same value.
5005 See also "ParamTypes" below.
5006 The "ParamValues" attribute was added in DBI 1.28.
5008 "ParamTypes"
5010 Type: hash ref, read-only
5012 Returns a reference to a hash containing the type information currently
5014 bound to placeholders. Returns undef if not supported by the driver.
5015 * Keys:
5017 See "ParamValues" above.
5019 * Values:
5021 The hash values are hashrefs of type information in the same form as
5023 that passed to the various bind_param() methods (See "bind_param" for
5024 the format and values).
5025 It is possible that the values in the hash returned by "ParamTypes" are
5027 not exactly the same as those passed to bind_param() or execute().
5028 Param attributes specified using the abbreviated form, like this:
5029 $sth->bind_param(1, SQL_INTEGER);
5031 are returned in the expanded form, as if called like this:
5033 $sth->bind_param(1, { TYPE => SQL_INTEGER });
5035 The driver may have modified the type information in some way based on
5037 the bound values, other hints provided by the prepare()'d SQL
5038 statement, or alternate type mappings required by the driver or target
5039 database system. The driver may also add private keys (with names
5040 beginning with the drivers reserved prefix, e.g., odbc_xxx).
5041 * Example:
5043 The keys and values in the returned hash can be passed to the various
5045 bind_param() methods to effectively reproduce a previous param binding.
5046 For example:
5047 # assuming $sth1 is a previously prepared statement handle
5049 my $sth2 = $dbh->prepare( $sth1->{Statement} );
5050 my $ParamValues = $sth1->{ParamValues} || {};
5051 my $ParamTypes = $sth1->{ParamTypes} || {};
5052 $sth2->bind_param($_, $ParamValues->{$_}, $ParamTypes->{$_})
5053 for keys %{ {%$ParamValues, %$ParamTypes} };
5054 $sth2->execute();
5055 The "ParamTypes" attribute was added in DBI 1.49. Implementation is the
5057 responsibility of individual drivers; the DBI layer default
5058 implementation simply returns undef.
5059 "ParamArrays"
5061 Type: hash ref, read-only
5063 Returns a reference to a hash containing the values currently bound to
5065 placeholders with "execute_array" or "bind_param_array". The keys of
5066 the hash are the 'names' of the placeholders, typically integers
5067 starting at 1. Returns undef if not supported by the driver or no
5068 arrays of parameters are bound.
5069 Each key value is an array reference containing a list of the bound
5071 parameters for that column.
5072 For example:
5074 $sth = $dbh->prepare("INSERT INTO staff (id, name) values (?,?)");
5076 $sth->execute_array({},[1,2], ['fred','dave']);
5077 if ($sth->{ParamArrays}) {
5078 foreach $param (keys %{$sth->{ParamArrays}}) {
5079 printf "Parameters for %s : %s\n", $param,
5080 join(",", @{$sth->{ParamArrays}->{$param}});
5081 }
5082 }
5083 It is possible that the values in the hash returned by "ParamArrays"
5085 are not exactly the same as those passed to "bind_param_array" or
5086 "execute_array". The driver may have slightly modified values in some
5087 way based on the TYPE the value was bound with. For example a floating
5088 point value bound as an SQL_INTEGER type may be returned as an integer.
5089 It is also possible that the keys in the hash returned by "ParamArrays"
5091 are not exactly the same as those implied by the prepared statement.
5092 For example, DBD::Oracle translates '"?"' placeholders into '":pN"'
5093 where N is a sequence number starting at 1.
5094 "RowsInCache"
5096 Type: integer, read-only
5098 If the driver supports a local row cache for "SELECT" statements, then
5100 this attribute holds the number of un-fetched rows in the cache. If the
5101 driver doesn't, then it returns "undef". Note that some drivers pre-
5102 fetch rows on execute, whereas others wait till the first fetch.
5103 See also the "RowCacheSize" database handle attribute.
5105
5107 Catalog Methods
5108 An application can retrieve metadata information from the DBMS by
5109 issuing appropriate queries on the views of the Information Schema.
5110 Unfortunately, "INFORMATION_SCHEMA" views are seldom supported by the
5111 DBMS. Special methods (catalog methods) are available to return result
5112 sets for a small but important portion of that metadata:
5113 column_info
5115 foreign_key_info
5116 primary_key_info
5117 table_info
5118 statistics_info
5119 All catalog methods accept arguments in order to restrict the result
5121 sets. Passing "undef" to an optional argument does not constrain the
5122 search for that argument. However, an empty string ('') is treated as
5123 a regular search criteria and will only match an empty value.
5124 Note: SQL/CLI and ODBC differ in the handling of empty strings. An
5126 empty string will not restrict the result set in SQL/CLI.
5127 Most arguments in the catalog methods accept only ordinary values, e.g.
5129 the arguments of "primary_key_info()". Such arguments are treated as a
5130 literal string, i.e. the case is significant and quote characters are
5131 taken literally.
5132 Some arguments in the catalog methods accept search patterns (strings
5134 containing '_' and/or '%'), e.g. the $table argument of
5135 "column_info()". Passing '%' is equivalent to leaving the argument
5136 "undef".
5137 Caveat: The underscore ('_') is valid and often used in SQL
5139 identifiers. Passing such a value to a search pattern argument may
5140 return more rows than expected! To include pattern characters as
5141 literals, they must be preceded by an escape character which can be
5142 achieved with
5143 $esc = $dbh->get_info( 14 ); # SQL_SEARCH_PATTERN_ESCAPE
5145 $search_pattern =~ s/([_%])/$esc$1/g;
5146 The ODBC and SQL/CLI specifications define a way to change the default
5148 behaviour described above: All arguments (except list value arguments)
5149 are treated as identifier if the "SQL_ATTR_METADATA_ID" attribute is
5150 set to "SQL_TRUE". Quoted identifiers are very similar to ordinary
5151 values, i.e. their body (the string within the quotes) is interpreted
5152 literally. Unquoted identifiers are compared in UPPERCASE.
5153 The DBI (currently) does not support the "SQL_ATTR_METADATA_ID"
5155 attribute, i.e. it behaves like an ODBC driver where
5156 "SQL_ATTR_METADATA_ID" is set to "SQL_FALSE".
5157 Transactions
5159 Transactions are a fundamental part of any robust database system. They
5160 protect against errors and database corruption by ensuring that sets of
5161 related changes to the database take place in atomic (indivisible, all-
5162 or-nothing) units.
5163 This section applies to databases that support transactions and where
5165 "AutoCommit" is off. See "AutoCommit" for details of using
5166 "AutoCommit" with various types of databases.
5167 The recommended way to implement robust transactions in Perl
5169 applications is to enable "RaiseError" and catch the error that's
5170 'thrown' as an exception. For example, using Try::Tiny:
5171 use Try::Tiny;
5173 $dbh->{AutoCommit} = 0; # enable transactions, if possible
5174 $dbh->{RaiseError} = 1;
5175 try {
5176 foo(...) # do lots of work here
5177 bar(...) # including inserts
5178 baz(...) # and updates
5179 $dbh->commit; # commit the changes if we get this far
5180 } catch {
5181 warn "Transaction aborted because $_"; # Try::Tiny copies $@ into $_
5182 # now rollback to undo the incomplete changes
5183 # but do it in an eval{} as it may also fail
5184 eval { $dbh->rollback };
5185 # add other application on-error-clean-up code here
5186 };
5187 If the "RaiseError" attribute is not set, then DBI calls would need to
5189 be manually checked for errors, typically like this:
5190 $h->method(@args) or die $h->errstr;
5192 With "RaiseError" set, the DBI will automatically "die" if any DBI
5194 method call on that handle (or a child handle) fails, so you don't have
5195 to test the return value of each method call. See "RaiseError" for more
5196 details.
5197 A major advantage of the "eval" approach is that the transaction will
5199 be properly rolled back if any code (not just DBI calls) in the inner
5200 application dies for any reason. The major advantage of using the
5201 "$h->{RaiseError}" attribute is that all DBI calls will be checked
5202 automatically. Both techniques are strongly recommended.
5203 After calling "commit" or "rollback" many drivers will not let you
5205 fetch from a previously active "SELECT" statement handle that's a child
5206 of the same database handle. A typical way round this is to connect the
5207 the database twice and use one connection for "SELECT" statements.
5208 See "AutoCommit" and "disconnect" for other important information about
5210 transactions.
5211 Handling BLOB / LONG / Memo Fields
5213 Many databases support "blob" (binary large objects), "long", or
5214 similar datatypes for holding very long strings or large amounts of
5215 binary data in a single field. Some databases support variable length
5216 long values over 2,000,000,000 bytes in length.
5217 Since values of that size can't usually be held in memory, and because
5219 databases can't usually know in advance the length of the longest long
5220 that will be returned from a "SELECT" statement (unlike other data
5221 types), some special handling is required.
5222 In this situation, the value of the "$h->{LongReadLen}" attribute is
5224 used to determine how much buffer space to allocate when fetching such
5225 fields. The "$h->{LongTruncOk}" attribute is used to determine how to
5226 behave if a fetched value can't fit into the buffer.
5227 See the description of "LongReadLen" for more information.
5229 When trying to insert long or binary values, placeholders should be
5231 used since there are often limits on the maximum size of an "INSERT"
5232 statement and the "quote" method generally can't cope with binary data.
5233 See "Placeholders and Bind Values".
5234 Simple Examples
5236 Here's a complete example program to select and fetch some data:
5237 my $data_source = "dbi::DriverName:db_name";
5239 my $dbh = DBI->connect($data_source, $user, $password)
5240 or die "Can't connect to $data_source: $DBI::errstr";
5241 my $sth = $dbh->prepare( q{
5243 SELECT name, phone
5244 FROM mytelbook
5245 }) or die "Can't prepare statement: $DBI::errstr";
5246 my $rc = $sth->execute
5248 or die "Can't execute statement: $DBI::errstr";
5249 print "Query will return $sth->{NUM_OF_FIELDS} fields.\n\n";
5251 print "Field names: @{ $sth->{NAME} }\n";
5252 while (($name, $phone) = $sth->fetchrow_array) {
5254 print "$name: $phone\n";
5255 }
5256 # check for problems which may have terminated the fetch early
5257 die $sth->errstr if $sth->err;
5258 $dbh->disconnect;
5260 Here's a complete example program to insert some data from a file.
5262 (This example uses "RaiseError" to avoid needing to check each call).
5263 my $dbh = DBI->connect("dbi:DriverName:db_name", $user, $password, {
5265 RaiseError => 1, AutoCommit => 0
5266 });
5267 my $sth = $dbh->prepare( q{
5269 INSERT INTO table (name, phone) VALUES (?, ?)
5270 });
5271 open FH, "<phone.csv" or die "Unable to open phone.csv: $!";
5273 while (<FH>) {
5274 chomp;
5275 my ($name, $phone) = split /,/;
5276 $sth->execute($name, $phone);
5277 }
5278 close FH;
5279 $dbh->commit;
5281 $dbh->disconnect;
5282 Here's how to convert fetched NULLs (undefined values) into empty
5284 strings:
5285 while($row = $sth->fetchrow_arrayref) {
5287 # this is a fast and simple way to deal with nulls:
5288 foreach (@$row) { $_ = '' unless defined }
5289 print "@$row\n";
5290 }
5291 The "q{...}" style quoting used in these examples avoids clashing with
5293 quotes that may be used in the SQL statement. Use the double-quote like
5294 "qq{...}" operator if you want to interpolate variables into the
5295 string. See "Quote and Quote-like Operators" in perlop for more
5296 details.
5297 Threads and Thread Safety
5299 Perl 5.7 and later support a new threading model called iThreads. (The
5300 old "5.005 style" threads are not supported by the DBI.)
5301 In the iThreads model each thread has its own copy of the perl
5303 interpreter. When a new thread is created the original perl
5304 interpreter is 'cloned' to create a new copy for the new thread.
5305 If the DBI and drivers are loaded and handles created before the thread
5307 is created then it will get a cloned copy of the DBI, the drivers and
5308 the handles.
5309 However, the internal pointer data within the handles will refer to the
5311 DBI and drivers in the original interpreter. Using those handles in the
5312 new interpreter thread is not safe, so the DBI detects this and croaks
5313 on any method call using handles that don't belong to the current
5314 thread (except for DESTROY).
5315 Because of this (possibly temporary) restriction, newly created threads
5317 must make their own connections to the database. Handles can't be
5318 shared across threads.
5319 But BEWARE, some underlying database APIs (the code the DBD driver uses
5321 to talk to the database, often supplied by the database vendor) are not
5322 thread safe. If it's not thread safe, then allowing more than one
5323 thread to enter the code at the same time may cause subtle/serious
5324 problems. In some cases allowing more than one thread to enter the
5325 code, even if not at the same time, can cause problems. You have been
5326 warned.
5327 Using DBI with perl threads is not yet recommended for production
5329 environments. For more information see
5330 <http://www.perlmonks.org/index.pl?node_id=288022>
5331 Note: There is a bug in perl 5.8.2 when configured with threads and
5333 debugging enabled (bug #24463) which causes a DBI test to fail.
5334 Signal Handling and Canceling Operations
5336 [The following only applies to systems with unix-like signal handling.
5337 I'd welcome additions for other systems, especially Windows.]
5338 The first thing to say is that signal handling in Perl versions less
5340 than 5.8 is not safe. There is always a small risk of Perl crashing
5341 and/or core dumping when, or after, handling a signal because the
5342 signal could arrive and be handled while internal data structures are
5343 being changed. If the signal handling code used those same internal
5344 data structures it could cause all manner of subtle and not-so-subtle
5345 problems. The risk was reduced with 5.4.4 but was still present in all
5346 perls up through 5.8.0.
5347 Beginning in perl 5.8.0 perl implements 'safe' signal handling if your
5349 system has the POSIX sigaction() routine. Now when a signal is
5350 delivered perl just makes a note of it but does not run the %SIG
5351 handler. The handling is 'deferred' until a 'safe' moment.
5352 Although this change made signal handling safe, it also lead to a
5354 problem with signals being deferred for longer than you'd like. If a
5355 signal arrived while executing a system call, such as waiting for data
5356 on a network connection, the signal is noted and then the system call
5357 that was executing returns with an EINTR error code to indicate that it
5358 was interrupted. All fine so far.
5359 The problem comes when the code that made the system call sees the
5361 EINTR code and decides it's going to call it again. Perl doesn't do
5362 that, but database code sometimes does. If that happens then the signal
5363 handler doesn't get called until later. Maybe much later.
5364 Fortunately there are ways around this which we'll discuss below.
5366 Unfortunately they make signals unsafe again.
5367 The two most common uses of signals in relation to the DBI are for
5369 canceling operations when the user types Ctrl-C (interrupt), and for
5370 implementing a timeout using "alarm()" and $SIG{ALRM}.
5371 Cancel
5373 The DBI provides a "cancel" method for statement handles. The
5374 "cancel" method should abort the current operation and is designed
5375 to be called from a signal handler. For example:
5376 $SIG{INT} = sub { $sth->cancel };
5378 However, few drivers implement this (the DBI provides a default
5380 method that just returns "undef") and, even if implemented, there
5381 is still a possibility that the statement handle, and even the
5382 parent database handle, will not be usable afterwards.
5383 If "cancel" returns true, then it has successfully invoked the
5385 database engine's own cancel function. If it returns false, then
5386 "cancel" failed. If it returns "undef", then the database driver
5387 does not have cancel implemented - very few do.
5388 Timeout
5390 The traditional way to implement a timeout is to set $SIG{ALRM} to
5391 refer to some code that will be executed when an ALRM signal
5392 arrives and then to call alarm($seconds) to schedule an ALRM signal
5393 to be delivered $seconds in the future. For example:
5394 my $failed;
5396 eval {
5397 local $SIG{ALRM} = sub { die "TIMEOUT\n" }; # N.B. \n required
5398 eval {
5399 alarm($seconds);
5400 ... code to execute with timeout here (which may die) ...
5401 1;
5402 } or $failed = 1;
5403 # outer eval catches alarm that might fire JUST before this alarm(0)
5404 alarm(0); # cancel alarm (if code ran fast)
5405 die "$@" if $failed;
5406 1;
5407 } or $failed = 1;
5408 if ( $failed ) {
5409 if ( defined $@ and $@ eq "TIMEOUT\n" ) { ... }
5410 else { ... } # some other error
5411 }
5412 The first (outer) eval is used to avoid the unlikely but possible
5414 chance that the "code to execute" dies and the alarm fires before
5415 it is cancelled. Without the outer eval, if this happened your
5416 program will die if you have no ALRM handler or a non-local alarm
5417 handler will be called.
5418 Unfortunately, as described above, this won't always work as
5420 expected, depending on your perl version and the underlying
5421 database code.
5422 With Oracle for instance (DBD::Oracle), if the system which hosts
5424 the database is down the DBI->connect() call will hang for several
5425 minutes before returning an error.
5426 The solution on these systems is to use the "POSIX::sigaction()"
5428 routine to gain low level access to how the signal handler is
5429 installed.
5430 The code would look something like this (for the DBD-Oracle connect()):
5432 use POSIX qw(:signal_h);
5434 my $mask = POSIX::SigSet->new( SIGALRM ); # signals to mask in the handler
5436 my $action = POSIX::SigAction->new(
5437 sub { die "connect timeout\n" }, # the handler code ref
5438 $mask,
5439 # not using (perl 5.8.2 and later) 'safe' switch or sa_flags
5440 );
5441 my $oldaction = POSIX::SigAction->new();
5442 sigaction( SIGALRM, $action, $oldaction );
5443 my $dbh;
5444 my $failed;
5445 eval {
5446 eval {
5447 alarm(5); # seconds before time out
5448 $dbh = DBI->connect("dbi:Oracle:$dsn" ... );
5449 1;
5450 } or $failed = 1;
5451 alarm(0); # cancel alarm (if connect worked fast)
5452 die "$@\n" if $failed; # connect died
5453 1;
5454 } or $failed = 1;
5455 sigaction( SIGALRM, $oldaction ); # restore original signal handler
5456 if ( $failed ) {
5457 if ( defined $@ and $@ eq "connect timeout\n" ) {...}
5458 else { # connect died }
5459 }
5460 See previous example for the reasoning around the double eval.
5462 Similar techniques can be used for canceling statement execution.
5464 Unfortunately, this solution is somewhat messy, and it does not work
5466 with perl versions less than perl 5.8 where "POSIX::sigaction()"
5467 appears to be broken.
5468 For a cleaner implementation that works across perl versions, see
5470 Lincoln Baxter's Sys::SigAction module at Sys::SigAction. The
5471 documentation for Sys::SigAction includes an longer discussion of this
5472 problem, and a DBD::Oracle test script.
5473 Be sure to read all the signal handling sections of the perlipc manual.
5475 And finally, two more points to keep firmly in mind. Firstly, remember
5477 that what we've done here is essentially revert to old style unsafe
5478 handling of these signals. So do as little as possible in the handler.
5479 Ideally just die(). Secondly, the handles in use at the time the signal
5480 is handled may not be safe to use afterwards.
5481 Subclassing the DBI
5483 DBI can be subclassed and extended just like any other object oriented
5484 module. Before we talk about how to do that, it's important to be
5485 clear about the various DBI classes and how they work together.
5486 By default "$dbh = DBI->connect(...)" returns a $dbh blessed into the
5488 "DBI::db" class. And the "$dbh->prepare" method returns an $sth
5489 blessed into the "DBI::st" class (actually it simply changes the last
5490 four characters of the calling handle class to be "::st").
5491 The leading '"DBI"' is known as the 'root class' and the extra '"::db"'
5493 or '"::st"' are the 'handle type suffixes'. If you want to subclass the
5494 DBI you'll need to put your overriding methods into the appropriate
5495 classes. For example, if you want to use a root class of "MySubDBI"
5496 and override the do(), prepare() and execute() methods, then your do()
5497 and prepare() methods should be in the "MySubDBI::db" class and the
5498 execute() method should be in the "MySubDBI::st" class.
5499 To setup the inheritance hierarchy the @ISA variable in "MySubDBI::db"
5501 should include "DBI::db" and the @ISA variable in "MySubDBI::st" should
5502 include "DBI::st". The "MySubDBI" root class itself isn't currently
5503 used for anything visible and so, apart from setting @ISA to include
5504 "DBI", it can be left empty.
5505 So, having put your overriding methods into the right classes, and
5507 setup the inheritance hierarchy, how do you get the DBI to use them?
5508 You have two choices, either a static method call using the name of
5509 your subclass:
5510 $dbh = MySubDBI->connect(...);
5512 or specifying a "RootClass" attribute:
5514 $dbh = DBI->connect(..., { RootClass => 'MySubDBI' });
5516 If both forms are used then the attribute takes precedence.
5518 The only differences between the two are that using an explicit
5520 RootClass attribute will a) make the DBI automatically attempt to load
5521 a module by that name if the class doesn't exist, and b) won't call
5522 your MySubDBI::connect() method, if you have one.
5523 When subclassing is being used then, after a successful new connect,
5525 the DBI->connect method automatically calls:
5526 $dbh->connected($dsn, $user, $pass, \%attr);
5528 The default method does nothing. The call is made just to simplify any
5530 post-connection setup that your subclass may want to perform. The
5531 parameters are the same as passed to DBI->connect. If your subclass
5532 supplies a connected method, it should be part of the MySubDBI::db
5533 package.
5534 One more thing to note: you must let the DBI do the handle creation.
5536 If you want to override the connect() method in your *::dr class then
5537 it must still call SUPER::connect to get a $dbh to work with.
5538 Similarly, an overridden prepare() method in *::db must still call
5539 SUPER::prepare to get a $sth. If you try to create your own handles
5540 using bless() then you'll find the DBI will reject them with an "is not
5541 a DBI handle (has no magic)" error.
5542 Here's a brief example of a DBI subclass. A more thorough example can
5544 be found in t/subclass.t in the DBI distribution.
5545 package MySubDBI;
5547 use strict;
5549 use DBI;
5551 use vars qw(@ISA);
5552 @ISA = qw(DBI);
5553 package MySubDBI::db;
5555 use vars qw(@ISA);
5556 @ISA = qw(DBI::db);
5557 sub prepare {
5559 my ($dbh, @args) = @_;
5560 my $sth = $dbh->SUPER::prepare(@args)
5561 or return;
5562 $sth->{private_mysubdbi_info} = { foo => 'bar' };
5563 return $sth;
5564 }
5565 package MySubDBI::st;
5567 use vars qw(@ISA);
5568 @ISA = qw(DBI::st);
5569 sub fetch {
5571 my ($sth, @args) = @_;
5572 my $row = $sth->SUPER::fetch(@args)
5573 or return;
5574 do_something_magical_with_row_data($row)
5575 or return $sth->set_err(1234, "The magic failed", undef, "fetch");
5576 return $row;
5577 }
5578 When calling a SUPER::method that returns a handle, be careful to check
5580 the return value before trying to do other things with it in your
5581 overridden method. This is especially important if you want to set a
5582 hash attribute on the handle, as Perl's autovivification will bite you
5583 by (in)conveniently creating an unblessed hashref, which your method
5584 will then return with usually baffling results later on like the error
5585 "dbih_getcom handle HASH(0xa4451a8) is not a DBI handle (has no magic".
5586 It's best to check right after the call and return undef immediately on
5587 error, just like DBI would and just like the example above.
5588 If your method needs to record an error it should call the set_err()
5590 method with the error code and error string, as shown in the example
5591 above. The error code and error string will be recorded in the handle
5592 and available via "$h->err" and $DBI::errstr etc. The set_err() method
5593 always returns an undef or empty list as appropriate. Since your method
5594 should nearly always return an undef or empty list as soon as an error
5595 is detected it's handy to simply return what set_err() returns, as
5596 shown in the example above.
5597 If the handle has "RaiseError", "PrintError", or "HandleError" etc. set
5599 then the set_err() method will honour them. This means that if
5600 "RaiseError" is set then set_err() won't return in the normal way but
5601 will 'throw an exception' that can be caught with an "eval" block.
5602 You can stash private data into DBI handles via "$h->{private_..._*}".
5604 See the entry under "ATTRIBUTES COMMON TO ALL HANDLES" for info and
5605 important caveats.
5606 Memory Leaks
5608 When tracking down memory leaks using tools like Devel::Leak you'll
5609 find that some DBI internals are reported as 'leaking' memory. This is
5610 very unlikely to be a real leak. The DBI has various caches to improve
5611 performance and the apparrent leaks are simply the normal operation of
5612 these caches.
5613 The most frequent sources of the apparrent leaks are "ChildHandles",
5615 "prepare_cached" and "connect_cached".
5616 For example
5618 http://stackoverflow.com/questions/13338308/perl-dbi-memory-leak
5619 Given how widely the DBI is used, you can rest assured that if a new
5621 release of the DBI did have a real leak it would be discovered,
5622 reported, and fixed immediately. The leak you're looking for is
5623 probably elsewhere. Good luck!
5624
5626 The DBI has a powerful tracing mechanism built in. It enables you to
5627 see what's going on 'behind the scenes', both within the DBI and the
5628 drivers you're using.
5629 Trace Settings
5631 Which details are written to the trace output is controlled by a
5632 combination of a trace level, an integer from 0 to 15, and a set of
5633 trace flags that are either on or off. Together these are known as the
5634 trace settings and are stored together in a single integer. For normal
5635 use you only need to set the trace level, and generally only to a value
5636 between 1 and 4.
5637 Each handle has its own trace settings, and so does the DBI. When you
5639 call a method the DBI merges the handles settings into its own for the
5640 duration of the call: the trace flags of the handle are OR'd into the
5641 trace flags of the DBI, and if the handle has a higher trace level then
5642 the DBI trace level is raised to match it. The previous DBI trace
5643 settings are restored when the called method returns.
5644 Trace Levels
5646 Trace levels are as follows:
5647 0 - Trace disabled.
5649 1 - Trace top-level DBI method calls returning with results or errors.
5650 2 - As above, adding tracing of top-level method entry with parameters.
5651 3 - As above, adding some high-level information from the driver
5652 and some internal information from the DBI.
5653 4 - As above, adding more detailed information from the driver.
5654 This is the first level to trace all the rows being fetched.
5655 5 to 15 - As above but with more and more internal information.
5656 Trace level 1 is best for a simple overview of what's happening. Trace
5658 levels 2 thru 4 a good choice for general purpose tracing. Levels 5
5659 and above are best reserved for investigating a specific problem, when
5660 you need to see "inside" the driver and DBI.
5661 The trace output is detailed and typically very useful. Much of the
5663 trace output is formatted using the "neat" function, so strings in the
5664 trace output may be edited and truncated by that function.
5665 Trace Flags
5667 Trace flags are used to enable tracing of specific activities within
5668 the DBI and drivers. The DBI defines some trace flags and drivers can
5669 define others. DBI trace flag names begin with a capital letter and
5670 driver specific names begin with a lowercase letter, as usual.
5671 Currently the DBI defines these trace flags:
5673 ALL - turn on all DBI and driver flags (not recommended)
5675 SQL - trace SQL statements executed
5676 (not yet implemented in DBI but implemented in some DBDs)
5677 CON - trace connection process
5678 ENC - trace encoding (unicode translations etc)
5679 (not yet implemented in DBI but implemented in some DBDs)
5680 DBD - trace only DBD messages
5681 (not implemented by all DBDs yet)
5682 TXN - trace transactions
5683 (not implemented in all DBDs yet)
5684 The "parse_trace_flags" and "parse_trace_flag" methods are used to
5686 convert trace flag names into the corresponding integer bit flags.
5687 Enabling Trace
5689 The "$h->trace" method sets the trace settings for a handle and
5690 "DBI->trace" does the same for the DBI.
5691 In addition to the "trace" method, you can enable the same trace
5693 information, and direct the output to a file, by setting the
5694 "DBI_TRACE" environment variable before starting Perl. See "DBI_TRACE"
5695 for more information.
5696 Finally, you can set, or get, the trace settings for a handle using the
5698 "TraceLevel" attribute.
5699 All of those methods use parse_trace_flags() and so allow you set both
5701 the trace level and multiple trace flags by using a string containing
5702 the trace level and/or flag names separated by vertical bar (""|"") or
5703 comma ("","") characters. For example:
5704 local $h->{TraceLevel} = "3|SQL|foo";
5706 Trace Output
5708 Initially trace output is written to "STDERR". Both the "$h->trace"
5709 and "DBI->trace" methods take an optional $trace_file parameter, which
5710 may be either the name of a file to be opened by DBI in append mode, or
5711 a reference to an existing writable (possibly layered) filehandle. If
5712 $trace_file is a filename, and can be opened in append mode, or
5713 $trace_file is a writable filehandle, then all trace output (currently
5714 including that from other handles) is redirected to that file. A
5715 warning is generated if $trace_file can't be opened or is not writable.
5716 Further calls to trace() without $trace_file do not alter where the
5718 trace output is sent. If $trace_file is undefined, then trace output is
5719 sent to "STDERR" and, if the prior trace was opened with $trace_file as
5720 a filename, the previous trace file is closed; if $trace_file was a
5721 filehandle, the filehandle is not closed.
5722 NOTE: If $trace_file is specified as a filehandle, the filehandle
5724 should not be closed until all DBI operations are completed, or the
5725 application has reset the trace file via another call to "trace()" that
5726 changes the trace file.
5727 Tracing to Layered Filehandles
5729 NOTE:
5730 · Tied filehandles are not currently supported, as tie operations are
5732 not available to the PerlIO methods used by the DBI.
5733 · PerlIO layer support requires Perl version 5.8 or higher.
5735 As of version 5.8, Perl provides the ability to layer various
5737 "disciplines" on an open filehandle via the PerlIO module.
5738 A simple example of using PerlIO layers is to use a scalar as the
5740 output:
5741 my $scalar = '';
5743 open( my $fh, "+>:scalar", \$scalar );
5744 $dbh->trace( 2, $fh );
5745 Now all trace output is simply appended to $scalar.
5747 A more complex application of tracing to a layered filehandle is the
5749 use of a custom layer (Refer to Perlio::via for details on creating
5750 custom PerlIO layers.). Consider an application with the following
5751 logger module:
5752 package MyFancyLogger;
5754 sub new
5756 {
5757 my $self = {};
5758 my $fh;
5759 open $fh, '>', 'fancylog.log';
5760 $self->{_fh} = $fh;
5761 $self->{_buf} = '';
5762 return bless $self, shift;
5763 }
5764 sub log
5766 {
5767 my $self = shift;
5768 return unless exists $self->{_fh};
5769 my $fh = $self->{_fh};
5770 $self->{_buf} .= shift;
5771 #
5772 # DBI feeds us pieces at a time, so accumulate a complete line
5773 # before outputing
5774 #
5775 print $fh "At ", scalar localtime(), ':', $self->{_buf}, "\n" and
5776 $self->{_buf} = ''
5777 if $self->{_buf}=~tr/\n//;
5778 }
5779 sub close {
5781 my $self = shift;
5782 return unless exists $self->{_fh};
5783 my $fh = $self->{_fh};
5784 print $fh "At ", scalar localtime(), ':', $self->{_buf}, "\n" and
5785 $self->{_buf} = ''
5786 if $self->{_buf};
5787 close $fh;
5788 delete $self->{_fh};
5789 }
5790 1;
5792 To redirect DBI traces to this logger requires creating a package for
5794 the layer:
5795 package PerlIO::via::MyFancyLogLayer;
5797 sub PUSHED
5799 {
5800 my ($class,$mode,$fh) = @_;
5801 my $logger;
5802 return bless \$logger,$class;
5803 }
5804 sub OPEN {
5806 my ($self, $path, $mode, $fh) = @_;
5807 #
5808 # $path is actually our logger object
5809 #
5810 $$self = $path;
5811 return 1;
5812 }
5813 sub WRITE
5815 {
5816 my ($self, $buf, $fh) = @_;
5817 $$self->log($buf);
5818 return length($buf);
5819 }
5820 sub CLOSE {
5822 my $self = shift;
5823 $$self->close();
5824 return 0;
5825 }
5826 1;
5828 The application can then cause DBI traces to be routed to the logger
5830 using
5831 use PerlIO::via::MyFancyLogLayer;
5833 open my $fh, '>:via(MyFancyLogLayer)', MyFancyLogger->new();
5835 $dbh->trace('SQL', $fh);
5837 Now all trace output will be processed by MyFancyLogger's log() method.
5839 Trace Content
5841 Many of the values embedded in trace output are formatted using the
5842 neat() utility function. This means they may be quoted, sanitized, and
5843 possibly truncated if longer than $DBI::neat_maxlen. See "neat" for
5844 more details.
5845 Tracing Tips
5847 You can add tracing to your own application code using the "trace_msg"
5848 method.
5849 It can sometimes be handy to compare trace files from two different
5851 runs of the same script. However using a tool like "diff" on the
5852 original log output doesn't work well because the trace file is full of
5853 object addresses that may differ on each run.
5854 The DBI includes a handy utility called dbilogstrip that can be used to
5856 'normalize' the log content. It can be used as a filter like this:
5857 DBI_TRACE=2 perl yourscript.pl ...args1... 2>&1 | dbilogstrip > dbitrace1.log
5859 DBI_TRACE=2 perl yourscript.pl ...args2... 2>&1 | dbilogstrip > dbitrace2.log
5860 diff -u dbitrace1.log dbitrace2.log
5861 See dbilogstrip for more information.
5863
5865 The DBI module recognizes a number of environment variables, but most
5866 of them should not be used most of the time. It is better to be
5867 explicit about what you are doing to avoid the need for environment
5868 variables, especially in a web serving system where web servers are
5869 stingy about which environment variables are available.
5870 DBI_DSN
5872 The DBI_DSN environment variable is used by DBI->connect if you do not
5873 specify a data source when you issue the connect. It should have a
5874 format such as "dbi:Driver:databasename".
5875 DBI_DRIVER
5877 The DBI_DRIVER environment variable is used to fill in the database
5878 driver name in DBI->connect if the data source string starts "dbi::"
5879 (thereby omitting the driver). If DBI_DSN omits the driver name,
5880 DBI_DRIVER can fill the gap.
5881 DBI_AUTOPROXY
5883 The DBI_AUTOPROXY environment variable takes a string value that starts
5884 "dbi:Proxy:" and is typically followed by "hostname=...;port=...". It
5885 is used to alter the behaviour of DBI->connect. For full details, see
5886 DBI::Proxy documentation.
5887 DBI_USER
5889 The DBI_USER environment variable takes a string value that is used as
5890 the user name if the DBI->connect call is given undef (as distinct from
5891 an empty string) as the username argument. Be wary of the security
5892 implications of using this.
5893 DBI_PASS
5895 The DBI_PASS environment variable takes a string value that is used as
5896 the password if the DBI->connect call is given undef (as distinct from
5897 an empty string) as the password argument. Be extra wary of the
5898 security implications of using this.
5899 DBI_DBNAME (obsolete)
5901 The DBI_DBNAME environment variable takes a string value that is used
5902 only when the obsolescent style of DBI->connect (with driver name as
5903 fourth parameter) is used, and when no value is provided for the first
5904 (database name) argument.
5905 DBI_TRACE
5907 The DBI_TRACE environment variable specifies the global default trace
5908 settings for the DBI at startup. Can also be used to direct trace
5909 output to a file. When the DBI is loaded it does:
5910 DBI->trace(split /=/, $ENV{DBI_TRACE}, 2) if $ENV{DBI_TRACE};
5912 So if "DBI_TRACE" contains an ""="" character then what follows it is
5914 used as the name of the file to append the trace to.
5915 output appended to that file. If the name begins with a number followed
5917 by an equal sign ("="), then the number and the equal sign are stripped
5918 off from the name, and the number is used to set the trace level. For
5919 example:
5920 DBI_TRACE=1=dbitrace.log perl your_test_script.pl
5922 On Unix-like systems using a Bourne-like shell, you can do this easily
5924 on the command line:
5925 DBI_TRACE=2 perl your_test_script.pl
5927 See "TRACING" for more information.
5929 PERL_DBI_DEBUG (obsolete)
5931 An old variable that should no longer be used; equivalent to DBI_TRACE.
5932 DBI_PROFILE
5934 The DBI_PROFILE environment variable can be used to enable profiling of
5935 DBI method calls. See DBI::Profile for more information.
5936 DBI_PUREPERL
5938 The DBI_PUREPERL environment variable can be used to enable the use of
5939 DBI::PurePerl. See DBI::PurePerl for more information.
5940
5942 Fatal Errors
5943 Can't call method "prepare" without a package or object reference
5944 The $dbh handle you're using to call "prepare" is probably
5945 undefined because the preceding "connect" failed. You should always
5946 check the return status of DBI methods, or use the "RaiseError"
5947 attribute.
5948 Can't call method "execute" without a package or object reference
5950 The $sth handle you're using to call "execute" is probably
5951 undefined because the preceding "prepare" failed. You should always
5952 check the return status of DBI methods, or use the "RaiseError"
5953 attribute.
5954 DBI/DBD internal version mismatch
5956 The DBD driver module was built with a different version of DBI
5957 than the one currently being used. You should rebuild the DBD
5958 module under the current version of DBI.
5959 (Some rare platforms require "static linking". On those platforms,
5961 there may be an old DBI or DBD driver version actually embedded in
5962 the Perl executable being used.)
5963 DBD driver has not implemented the AutoCommit attribute
5965 The DBD driver implementation is incomplete. Consult the author.
5966 Can't [sg]et %s->{%s}: unrecognised attribute
5968 You attempted to set or get an unknown attribute of a handle. Make
5969 sure you have spelled the attribute name correctly; case is
5970 significant (e.g., "Autocommit" is not the same as "AutoCommit").
5971
5973 A pure-perl emulation of the DBI is included in the distribution for
5974 people using pure-perl drivers who, for whatever reason, can't install
5975 the compiled DBI. See DBI::PurePerl.
5976
5978 Driver and Database Documentation
5979 Refer to the documentation for the DBD driver that you are using.
5980 Refer to the SQL Language Reference Manual for the database engine that
5982 you are using.
5983 ODBC and SQL/CLI Standards Reference Information
5985 More detailed information about the semantics of certain DBI methods
5986 that are based on ODBC and SQL/CLI standards is available on-line via
5987 microsoft.com, for ODBC, and www.jtc1sc32.org for the SQL/CLI standard:
5988 DBI method ODBC function SQL/CLI Working Draft
5990 ---------- ------------- ---------------------
5991 column_info SQLColumns Page 124
5992 foreign_key_info SQLForeignKeys Page 163
5993 get_info SQLGetInfo Page 214
5994 primary_key_info SQLPrimaryKeys Page 254
5995 table_info SQLTables Page 294
5996 type_info SQLGetTypeInfo Page 239
5997 statistics_info SQLStatistics
5998 To find documentation on the ODBC function you can use the MSDN search
6000 facility at:
6001 http://msdn.microsoft.com/Search
6003 and search for something like "SQLColumns returns".
6005 And for SQL/CLI standard information on SQLColumns you'd read page 124
6007 of the (very large) SQL/CLI Working Draft available from:
6008 http://jtc1sc32.org/doc/N0701-0750/32N0744T.pdf
6010 Standards Reference Information
6012 A hyperlinked, browsable version of the BNF syntax for SQL92 (plus
6013 Oracle 7 SQL and PL/SQL) is available here:
6014 http://cui.unige.ch/db-research/Enseignement/analyseinfo/SQL92/BNFindex.html
6016 You can find more information about SQL standards online by searching
6018 for the appropriate standard names and numbers. For example, searching
6019 for "ANSI/ISO/IEC International Standard (IS) Database Language SQL -
6020 Part 1: SQL/Framework" you'll find a copy at:
6021 ftp://ftp.iks-jena.de/mitarb/lutz/standards/sql/ansi-iso-9075-1-1999.pdf
6023 Books and Articles
6025 Programming the Perl DBI, by Alligator Descartes and Tim Bunce.
6026 <http://books.perl.org/book/154>
6027 Programming Perl 3rd Ed. by Larry Wall, Tom Christiansen & Jon Orwant.
6029 <http://books.perl.org/book/134>
6030 Learning Perl by Randal Schwartz. <http://books.perl.org/book/101>
6032 Details of many other books related to perl can be found at
6034 <http://books.perl.org>
6035 Perl Modules
6037 Index of DBI related modules available from CPAN:
6038 L<https://metacpan.org/search?q=DBD%3A%3A>
6040 L<https://metacpan.org/search?q=DBIx%3A%3A>
6041 L<https://metacpan.org/search?q=DBI>
6042 For a good comparison of RDBMS-OO mappers and some OO-RDBMS mappers
6044 (including Class::DBI, Alzabo, and DBIx::RecordSet in the former
6045 category and Tangram and SPOPS in the latter) see the Perl Object-
6046 Oriented Persistence project pages at:
6047 http://poop.sourceforge.net
6049 A similar page for Java toolkits can be found at:
6051 http://c2.com/cgi-bin/wiki?ObjectRelationalToolComparison
6053 Mailing List
6055 The dbi-users mailing list is the primary means of communication among
6056 users of the DBI and its related modules. For details send email to:
6057 L<dbi-users-help@perl.org>
6059 There are typically between 700 and 900 messages per month. You have
6061 to subscribe in order to be able to post. However you can opt for a
6062 'post-only' subscription.
6063 Mailing list archives (of variable quality) are held at:
6065 http://groups.google.com/groups?group=perl.dbi.users
6067 http://www.xray.mpe.mpg.de/mailing-lists/dbi/
6068 http://www.mail-archive.com/dbi-users%40perl.org/
6069 Assorted Related Links
6071 The DBI "Home Page":
6072 http://dbi.perl.org/
6074 Other DBI related links:
6076 http://www.perlmonks.org/?node=DBI%20recipes
6078 http://www.perlmonks.org/?node=Speeding%20up%20the%20DBI
6079 Other database related links:
6081 http://www.connectionstrings.com/
6083 Security, especially the "SQL Injection" attack:
6085 http://bobby-tables.com/
6087 http://online.securityfocus.com/infocus/1644
6088 FAQ
6090 See <http://faq.dbi-support.com/>
6091
6093 DBI by Tim Bunce, <http://www.tim.bunce.name>
6094 This pod text by Tim Bunce, J. Douglas Dunlop, Jonathan Leffler and
6096 others. Perl by Larry Wall and the "perl5-porters".
6097
6099 The DBI module is Copyright (c) 1994-2012 Tim Bunce. Ireland. All
6100 rights reserved.
6101 You may distribute under the terms of either the GNU General Public
6103 License or the Artistic License, as specified in the Perl 5.10.0 README
6104 file.
6105
6107 The DBI is free Open Source software. IT COMES WITHOUT WARRANTY OF ANY
6108 KIND.
6109 Support
6111 My consulting company, Data Plan Services, offers annual and multi-
6112 annual support contracts for the DBI. These provide sustained support
6113 for DBI development, and sustained value for you in return. Contact me
6114 for details.
6115 Sponsor Enhancements
6117 If your company would benefit from a specific new DBI feature, please
6118 consider sponsoring its development. Work is performed rapidly, and
6119 usually on a fixed-price payment-on-delivery basis. Contact me for
6120 details.
6121 Using such targeted financing allows you to contribute to DBI
6123 development, and rapidly get something specific and valuable in return.
6124
6126 I would like to acknowledge the valuable contributions of the many
6127 people I have worked with on the DBI project, especially in the early
6128 years (1992-1994). In no particular order: Kevin Stock, Buzz Moschetti,
6129 Kurt Andersen, Ted Lemon, William Hails, Garth Kennedy, Michael
6130 Peppler, Neil S. Briscoe, Jeff Urlwin, David J. Hughes, Jeff Stander,
6131 Forrest D Whitcher, Larry Wall, Jeff Fried, Roy Johnson, Paul Hudson,
6132 Georg Rehfeld, Steve Sizemore, Ron Pool, Jon Meek, Tom Christiansen,
6133 Steve Baumgarten, Randal Schwartz, and a whole lot more.
6134 Then, of course, there are the poor souls who have struggled through
6136 untold and undocumented obstacles to actually implement DBI drivers.
6137 Among their ranks are Jochen Wiedmann, Alligator Descartes, Jonathan
6138 Leffler, Jeff Urlwin, Michael Peppler, Henrik Tougaard, Edwin Pratomo,
6139 Davide Migliavacca, Jan Pazdziora, Peter Haworth, Edmund Mergl, Steve
6140 Williams, Thomas Lowery, and Phlip Plumlee. Without them, the DBI would
6141 not be the practical reality it is today. I'm also especially grateful
6142 to Alligator Descartes for starting work on the first edition of the
6143 "Programming the Perl DBI" book and letting me jump on board.
6144 The DBI and DBD::Oracle were originally developed while I was Technical
6146 Director (CTO) of the Paul Ingram Group in the UK. So I'd especially
6147 like to thank Paul for his generosity and vision in supporting this
6148 work for many years.
6149 A couple of specific DBI features have been sponsored by enlightened
6151 companies:
6152 The development of the swap_inner_handle() method was sponsored by
6154 BizRate.com (<http://BizRate.com>)
6155 The development of DBD::Gofer and related modules was sponsored by
6157 Shopzilla.com (<http://Shopzilla.com>), where I currently work.
6158
6160 As you can see above, many people have contributed to the DBI and
6161 drivers in many ways over many years.
6162 If you'd like to help then see <http://dbi.perl.org/contributing>.
6164 If you'd like the DBI to do something new or different then a good way
6166 to make that happen is to do it yourself and send me a patch to the
6167 source code that shows the changes. (But read "Speak before you patch"
6168 below.)
6169 Browsing the source code repository
6171 Use https://github.com/perl5-dbi/dbi
6172 How to create a patch using Git
6174 The DBI source code is maintained using Git. To access the source
6175 you'll need to install a Git client. Then, to get the source code, do:
6176 git clone https://github.com/perl5-dbi/dbi.git DBI-git
6178 The source code will now be available in the new subdirectory
6180 "DBI-git".
6181 When you want to synchronize later, issue the command
6183 git pull --all
6185 Make your changes, test them, test them again until everything passes.
6187 If there are no tests for the new feature you added or a behaviour
6188 change, the change should include a new test. Then commit the changes.
6189 Either use
6190 git gui
6192 or
6194 git commit -a -m 'Message to my changes'
6196 If you get any conflicts reported you'll need to fix them first.
6198 Then generate the patch file to be mailed:
6200 git format-patch -1 --attach
6202 which will create a file 0001-*.patch (where * relates to the commit
6204 message). Read the patch file, as a sanity check, and then email it to
6205 dbi-dev@perl.org.
6206 If you have a github <https://github.com> account, you can also fork
6208 the repository, commit your changes to the forked repository and then
6209 do a pull request.
6210 How to create a patch without Git
6212 Unpack a fresh copy of the distribution:
6213 wget http://cpan.metacpan.org/authors/id/T/TI/TIMB/DBI-1.627.tar.gz
6215 tar xfz DBI-1.627.tar.gz
6216 Rename the newly created top level directory:
6218 mv DBI-1.627 DBI-1.627.your_foo
6220 Edit the contents of DBI-1.627.your_foo/* till it does what you want.
6222 Test your changes and then remove all temporary files:
6224 make test && make distclean
6226 Go back to the directory you originally unpacked the distribution:
6228 cd ..
6230 Unpack another copy of the original distribution you started with:
6232 tar xfz DBI-1.627.tar.gz
6234 Then create a patch file by performing a recursive "diff" on the two
6236 top level directories:
6237 diff -purd DBI-1.627 DBI-1.627.your_foo > DBI-1.627.your_foo.patch
6239 Speak before you patch
6241 For anything non-trivial or possibly controversial it's a good idea to
6242 discuss (on dbi-dev@perl.org) the changes you propose before actually
6243 spending time working on them. Otherwise you run the risk of them being
6244 rejected because they don't fit into some larger plans you may not be
6245 aware of.
6246 You can also reach the developers on IRC (chat). If they are on-line,
6248 the most likely place to talk to them is the #dbi channel on
6249 irc.perl.org
6250
6252 A German translation of this manual (possibly slightly out of date) is
6253 available, thanks to O'Reilly, at:
6254 http://www.oreilly.de/catalog/perldbiger/
6256
6258 References to DBI related training resources. No recommendation
6259 implied.
6260 http://www.treepax.co.uk/
6262 http://www.keller.com/dbweb/
6263 (If you offer professional DBI related training services, please send
6265 me your details so I can add them here.)
6266
6268 Apache::DBI
6269 To be used with the Apache daemon together with an embedded Perl
6270 interpreter like "mod_perl". Establishes a database connection
6271 which remains open for the lifetime of the HTTP daemon. This way
6272 the CGI connect and disconnect for every database access becomes
6273 superfluous.
6274 SQL Parser
6276 See also the SQL::Statement module, SQL parser and engine.
6277perl v5.26.3 2018-03-19 DBI(3)