1DBI::FAQ(3) User Contributed Perl Documentation DBI::FAQ(3)
2
6 DBI::FAQ -- The Frequently Asked Questions for the Perl5 Database
7 Interface
8
10 perldoc DBI::FAQ
11
13 This document is currently at version 0.38, as of February 8th, 2000.
14 That's very old. A newer FAQ can be found at
16 <http://faq.dbi-support.com/>
17 Neither this document nor that web site are actively maintained.
19 Volunteers are welcome.
20
22 This document serves to answer the most frequently asked questions on
23 both the DBI Mailing Lists and personally to members of the DBI
24 development team.
25
27 1.1 What is DBI, DBperl, Oraperl and *perl?
28 To quote Tim Bunce, the architect and author of DBI:
29 DBI is a database access Application Programming Interface (API)
31 for the Perl Language. The DBI API Specification defines a set
32 of functions, variables and conventions that provide a consistent
33 database interface independent of the actual database being used.
34 In simple language, the DBI interface allows users to access multiple
36 database types transparently. So, if you connecting to an Oracle,
37 Informix, mSQL, Sybase or whatever database, you don't need to know the
38 underlying mechanics of the 3GL layer. The API defined by DBI will work
39 on all these database types.
40 A similar benefit is gained by the ability to connect to two different
42 databases of different vendor within the one perl script, ie, I want to
43 read data from an Oracle database and insert it back into an Informix
44 database all within one program. The DBI layer allows you to do this
45 simply and powerfully.
46 DBperl is the old name for the interface specification. It's usually
48 now used to denote perl4 modules on database interfacing, such as,
49 oraperl, isqlperl, ingperl and so on. These interfaces didn't have a
50 standard API and are generally not supported.
51 Here's a list of DBperl modules, their corresponding DBI counterparts
53 and support information. Please note, the author's listed here
54 generally do not maintain the DBI module for the same database. These
55 email addresses are unverified and should only be used for queries
56 concerning the perl4 modules listed below. DBI driver queries should be
57 directed to the dbi-users mailing list.
58 Module Name Database Required Author DBI
60 ----------- ----------------- ------ ---
61 Sybperl Sybase Michael Peppler DBD::Sybase
62 <mpeppler@itf.ch>
63 Oraperl Oracle 6 & 7 Kevin Stock DBD::Oracle
64 <dbi-users@perl.org>
65 Ingperl Ingres Tim Bunce & DBD::Ingres
66 Ted Lemon
67 <dbi-users@perl.org>
68 Interperl Interbase Buzz Moschetti DBD::Interbase
69 <buzz@bear.com>
70 Uniperl Unify 5.0 Rick Wargo None
71 <rickers@coe.drexel.edu>
72 Pgperl Postgres Igor Metz DBD::Pg
73 <metz@iam.unibe.ch>
74 Btreeperl NDBM John Conover SDBM?
75 <john@johncon.com>
76 Ctreeperl C-Tree John Conover None
77 <john@johncon.com>
78 Cisamperl Informix C-ISAM Mathias Koerber None
79 <mathias@unicorn.swi.com.sg>
80 Duaperl X.500 Directory Eric Douglas None
81 User Agent
82 However, some DBI modules have DBperl emulation layers, so, DBD::Oracle
84 comes with an Oraperl emulation layer, which allows you to run legacy
85 oraperl scripts without modification. The emulation layer translates
86 the oraperl API calls into DBI calls and executes them through the DBI
87 switch.
88 Here's a table of emulation layer information:
90 Module Emulation Layer Status
92 ------ --------------- ------
93 DBD::Oracle Oraperl Complete
94 DBD::Informix Isqlperl Under development
95 DBD::Ingres Ingperl Complete?
96 DBD::Sybase Sybperl Working? ( Needs verification )
97 DBD::mSQL Msqlperl Experimentally released with
98 DBD::mSQL-0.61
99 The Msqlperl emulation is a special case. Msqlperl is a perl5 driver
101 for mSQL databases, but does not conform to the DBI Specification. It's
102 use is being deprecated in favour of DBD::mSQL. Msqlperl may be
103 downloaded from CPAN via:
104 http://www.perl.com/cgi-bin/cpan_mod?module=Msqlperl
106 1.2. Where can I get it from?
108 The Comprehensive Perl Archive Network resources should be used for
109 retrieving up-to-date versions of the DBI and drivers. CPAN may be
110 accessed via Tom Christiansen's splendid CPAN multiplexer program
111 located at:
112 http://www.perl.com/CPAN/
114 For more specific version information and exact URLs of drivers, please
116 see the DBI drivers list and the DBI module pages which can be found
117 on:
118 http://dbi.perl.org/
120 This list is automatically generated on a nightly basis from CPAN and
122 should be up-to-date.
123 1.3. Where can I get more information?
125 There are a few information sources on DBI.
126 "Programming the Perl DBI"
128 "Programming the Perl DBI" is the official book on the DBI written
129 by Alligator Descartes and Tim Bunce and published by O'Reilly &
130 Associates. The book was released on February 9th, 2000.
131 The table of contents is:
133 Preface
135 1. Introduction
136 From Mainframes to Workstations
137 Perl
138 DBI in the Real World
139 A Historical Interlude and Standing Stones
140 2. Basic Non-DBI Databases
141 Storage Managers and Layers
142 Query Languages and Data Functions
143 Standing Stones and the Sample Database
144 Flat-File Databases
145 Putting Complex Data into Flat Files
146 Concurrent Database Access and Locking
147 DBM Files and the Berkeley Database Manager
148 The MLDBM Module
149 Summary
150 3. SQL and Relational Databases
151 The Relational Database Methodology
152 Datatypes and NULL Values
153 Querying Data
154 Modifying Data Within Tables
155 Creating and Destroying Tables
156 4. Programming with the DBI
157 DBI Architecture
158 Handles
159 Data Source Names
160 Connection and Disconnection
161 Error Handling
162 Utility Methods and Functions
163 5. Interacting with the Database
164 Issuing Simple Queries
165 Executing Non-SELECT Statements
166 Binding Parameters to Statements
167 Binding Output Columns
168 do() Versus prepare()
169 Atomic and Batch Fetching
170 6. Advanced DBI
171 Handle Attributes and Metadata
172 Handling LONG/LOB Data
173 Transactions, Locking, and Isolation
174 7. ODBC and the DBI
175 ODBC -- Embraced and Extended
176 DBI -- Thrashed and Mutated
177 The Nuts and Bolts of ODBC
178 ODBC from Perl
179 The Marriage of DBI and ODBC
180 Questions and Choices
181 Moving Between Win32::ODBC and the DBI
182 And What About ADO?
183 8. DBI Shell and Database Proxying
184 dbish -- The DBI Shell
185 Database Proxying
186 A. DBI Specification
187 B. Driver and Database Characteristics
188 C. ASLaN Sacred Site Charter
189 Index
190 The book should be available from all good bookshops and can be
192 ordered online either <I>via</I> O'Reilly & Associates
193 http://www.oreilly.com/catalog/perldbi
195 or Amazon
197 http://www.amazon.com/exec/obidos/ASIN/1565926994/dbi
199 POD documentation
201 PODs are chunks of documentation usually embedded within perl
202 programs that document the code ``in place'', providing a useful
203 resource for programmers and users of modules. POD for DBI and
204 drivers is beginning to become more commonplace, and documentation
205 for these modules can be read with the "perldoc" program included
206 with Perl.
207 The DBI Specification
209 The POD for the DBI Specification can be read with the:
210 perldoc DBI
212 command. The Specification also forms Appendix A of
214 "Programming the Perl DBI".
215 Oraperl
217 Users of the Oraperl emulation layer bundled with DBD::Oracle,
218 may read up on how to program with the Oraperl interface by
219 typing:
220 perldoc Oraperl
222 This will produce an updated copy of the original oraperl man
224 page written by Kevin Stock for perl4. The oraperl API is fully
225 listed and described there.
226 Drivers
228 Users of the DBD modules may read about some of the private
229 functions and quirks of that driver by typing:
230 perldoc <driver>
232 For example, the DBD::mSQL driver is bundled with driver-
234 specific documentation that can be accessed by typing
235 perldoc DBD::mSQL
237 Frequently Asked Questions
239 This document, the Frequently Asked Questions is also available
240 as POD documentation! You can read this on your own system by
241 typing:
242 perldoc DBI::FAQ
244 This may be more convenient to persons not permanently, or
246 conveniently, connected to the Internet. The DBI::FAQ module
247 should be downloaded and installed for the more up-to-date
248 version.
249 The version of DBI::FAQ shipped with the "DBI" module may be
251 slightly out of date.
252 POD in general
254 Information on writing POD, and on the philosophy of POD in
255 general, can be read by typing:
256 perldoc perlpod
258 Users with the Tk module installed may be interested to learn
260 there is a Tk-based POD reader available called "tkpod", which
261 formats POD in a convenient and readable way. This is available
262 via CPAN as the module called Tk::POD and is highly
263 recommended.
264 Driver and Database Characteristics
266 The driver summaries that were produced for Appendix B of
267 "Programming the Perl DBI" are available online at:
268 http://dbi.perl.org/
270 in the driver information table. These summaries contain
272 standardised information on each driver and database which should
273 aid you in selecting a database to use. It will also inform you
274 quickly of any issues within drivers or whether a driver is not
275 fully compliant with the DBI Specification.
276 Rambles, Tidbits and Observations
278 http://dbi.perl.org/tidbits
279 There are a series of occasional rambles from various people on the
281 DBI mailing lists who, in an attempt to clear up a simple point,
282 end up drafting fairly comprehensive documents. These are quite
283 often varying in quality, but do provide some insights into the
284 workings of the interfaces.
285 Articles
287 A list of articles discussing the DBI can be found on the DBI WWW
288 page at:
289 http://dbi.perl.org/
291 These articles are of varying quality and age, from the original
293 Perl Journal article written by Alligator and Tim, to more recent
294 debacles published online from about.com.
295 README files
297 The README files included with each driver occasionally contains
298 some useful information ( no, really! ) that may be pertinent to
299 the user. Please read them. It makes our worthless existences more
300 bearable. These can all be read from the main DBI WWW page at:
301 http://dbi.perl.org/
303 Mailing Lists
305 There are three mailing lists for DBI:
306 dbi-announce@perl.org -- for announcements, very low traffic
308 dbi-users@perl.org -- general user support
309 dbi-dev@perl.org -- for driver developers (no user support)
310 For information on how to subscribe, set digest mode etc, and
312 unsubscribe, send an email message (the content will be ignored)
313 to:
314 dbi-announce-help@perl.org
316 dbi-users-help@perl.org
317 dbi-dev-help@perl.org
318 Mailing List Archives
320 US Mailing List Archives
321 http://outside.organic.com/mail-archives/dbi-users/
322 Searchable hypermail archives of the three mailing lists, and
324 some of the much older traffic have been set up for users to
325 browse.
326 European Mailing List Archives
328 http://www.rosat.mpe-garching.mpg.de/mailing-lists/PerlDB-Interest
329 As per the US archive above.
331
333 2.1. Compilation problems or "It fails the test!"
334 First off, consult the README for that driver in case there is useful
335 information about the problem. It may be a known problem for your given
336 architecture and operating system or database. You can check the README
337 files for each driver in advance online at:
338 http://dbi.perl.org/
340 If it's a known problem, you'll probably have to wait till it gets
342 fixed. If you're really needing it fixed, try the following:
343 Attempt to fix it yourself
345 This technique is generally not recommended to the faint-hearted.
346 If you do think you have managed to fix it, then, send a patch file
347 ( context diff ) to the author with an explanation of:
348 · What the problem was, and test cases, if possible.
350 · What you needed to do to fix it. Please make sure you mention
352 everything.
353 · Platform information, database version, perl version, module
355 version and DBI version.
356 Email the author Do NOT whinge!
358 Please email the address listed in the WWW pages for whichever
359 driver you are having problems with. Do not directly email the
360 author at a known address unless it corresponds with the one
361 listed.
362 We tend to have real jobs to do, and we do read the mailing lists
364 for problems. Besides, we may not have access to <insert your
365 favourite brain-damaged platform here> and couldn't be of any
366 assistance anyway! Apologies for sounding harsh, but that's the way
367 of it!
368 However, you might catch one of these creative genii at 3am when
370 we're doing this sort of stuff anyway, and get a patch within 5
371 minutes. The atmosphere in the DBI circle is that we do appreciate
372 the users' problems, since we work in similar environments.
373 If you are planning to email the author, please furnish as much
375 information as possible, ie:
376 · ALL the information asked for in the README file in the
378 problematic module. And we mean ALL of it. We don't put lines
379 like that in documentation for the good of our health, or to
380 meet obscure README file standards of length.
381 · If you have a core dump, try the Devel::CoreStack module for
383 generating a stack trace from the core dump. Send us that too.
384 Devel::CoreStack can be found on CPAN at:
385 http://www.perl.com/cgi-bin/cpan_mod?module=Devel::CoreStack
387 · Module versions, perl version, test cases, operating system
389 versions and any other pertinent information.
390 Remember, the more information you send us, the quicker we can
392 track problems down. If you send us no useful information, expect
393 nothing back.
394 Finally, please be aware that some authors, including Tim Bunce,
396 specifically request that you do not mail them directly. Please
397 respect their wishes and use the email addresses listed in the
398 appropriate module "README" file.
399 Email the dbi-users Mailing List
401 It's usually a fairly intelligent idea to cc the mailing list
402 anyway with problems. The authors all read the lists, so you lose
403 nothing by mailing there.
404
406 3.1 What's the difference between ODBC and DBI?
407 In terms of architecture - not much: Both define programming
408 interfaces. Both allow multiple drivers to be loaded to do the actual
409 work.
410 In terms of ease of use - much: The DBI is a 'high level' interface
412 that, like Perl itself, strives to make the simple things easy while
413 still making the hard things possible. The ODBC is a 'low level'
414 interface. All nuts-bolts-knobs-and-dials.
415 Now there's an ODBC driver for the DBI (DBD::ODBC) the "What's the
417 difference" question is more usefully rephrased as:
418 Chapter 7 of "Programming the Perl DBI" covers this topic in far more
420 detail and should be consulted.
421 3.2 What's the difference between Win32::ODBC and DBD::ODBC?
423 The DBI, and thus DBD::ODBC, has a different philosophy from the
424 Win32::ODBC module:
425 The Win32::ODBC module is a 'thin' layer over the low-level ODBC API.
427 The DBI defines a simpler 'higher level' interface.
428 The Win32::ODBC module gives you access to more of the ODBC API. The
430 DBI and DBD::ODBC give you access to only the essentials. (But, unlike
431 Win32::ODBC, the DBI and DBD::ODBC do support parameter binding and
432 multiple prepared statements which reduces the load on the database
433 server and can dramatically increase performance.)
434 The Win32::ODBC module only works on Win32 systems. The DBI and
436 DBD::ODBC are very portable and work on Win32 and Unix.
437 The DBI and DBD::ODBC modules are supplied as a standard part of the
439 Perl 5.004 binary distribution for Win32 (they don't work with the
440 older, non-standard, ActiveState port).
441 Scripts written with the DBI and DBD::ODBC are faster than Win32::ODBC
443 on Win32 and are trivially portable to other supported database types.
444 The DBI offers optional automatic printing or die()ing on errors which
446 makes applications simpler and more robust.
447 The current DBD::ODBC driver version 0.16 is new and not yet fully
449 stable. A new release is due soon [relative to the date of the next
450 TPJ issue :-] and will be much improved and offer more ODBC
451 functionality.
452 To summarise: The Win32::ODBC module is your best choice if you need
454 access to more of the ODBC API than the DBI gives you. Otherwise, the
455 DBI and DBD::ODBC combination may be your best bet.
456 Chapter 7 of "Programming the Perl DBI" covers this topic in far more
458 detail and should be consulted.
459 3.3 Is DBI supported under Windows 95 / NT platforms?
461 Finally, yes! Jeff Urlwin has been working diligently on building DBI
462 and DBD::ODBC under these platforms, and, with the advent of a stabler
463 perl and a port of MakeMaker, the project has come on by great leaps
464 and bounds.
465 The DBI and DBD::Oracle Win32 ports are now a standard part of DBI, so,
467 downloading DBI of version higher than 0.81 should work fine as should
468 using the most recent DBD::Oracle version.
469 3.4 Can I access Microsoft Access or SQL-Server databases with DBI?
471 Yes, use the DBD::ODBC driver.
472 3.5 Is there a DBD for <insert favourite database here>?
474 First check if a driver is available on CPAN by searching for the name
475 of the database (including common abbreviations and aliases).
476 Here's a general query that'll match all distributions:
478 http://search.cpan.org/search?query=DBD&mode=dist
480 If you can't find a driver that way, you could check if the database
482 supports ODBC drivers. If so then you could probably use the DBD::ODBC
483 driver:
484 http://search.cpan.org/dist/DBD-ODBC/
486 If not, then try asking on the dbi-users mailing list.
488 3.6 What's DBM? And why should I use DBI instead?
490 Extracted from ``DBI - The Database Interface for Perl 5'':
491 ``UNIX was originally blessed with simple file-based ``databases'', namely
493 the dbm system. dbm lets you store data in files, and retrieve
494 that data quickly. However, it also has serious drawbacks.
495 File Locking
497 The dbm systems did not allow particularly robust file locking
499 capabilities, nor any capability for correcting problems arising through
500 simultaneous writes [ to the database ].
501 Arbitrary Data Structures
503 The dbm systems only allows a single fixed data structure:
505 key-value pairs. That value could be a complex object, such as a
506 [ C ] struct, but the key had to be unique. This was a large
507 limitation on the usefulness of dbm systems.
508 However, dbm systems still provide a useful function for users with
510 simple datasets and limited resources, since they are fast, robust and
511 extremely well-tested. Perl modules to access dbm systems have now
512 been integrated into the core Perl distribution via the
513 AnyDBM_File module.''
514 To sum up, DBM is a perfectly satisfactory solution for essentially
516 read-only databases, or small and simple datasets. However, for more
517 scaleable dataset handling, not to mention robust transactional
518 locking, users are recommended to use a more powerful database engine
519 via DBI.
520 Chapter 2 of "Programming the Perl DBI" discusses DBM files in detail.
522 3.7 What database do you recommend me using?
524 This is a particularly thorny area in which an objective answer is
525 difficult to come by, since each dataset, proposed usage and system
526 configuration differs from person to person.
527 From the current author's point of view, if the dataset is relatively
529 small, being tables of less than 1 million rows, and less than 1000
530 tables in a given database, then mSQL is a perfectly acceptable
531 solution to your problem. This database is extremely cheap, is
532 wonderfully robust and has excellent support. More information is
533 available on the Hughes Technology WWW site at:
534 http://www.hughes.com.au
536 You may also wish to look at MySQL which is a more powerful database
538 engine that has a similar feel to mSQL.
539 http://www.tcx.se
541 If the dataset is larger than 1 million row tables or 1000 tables, or
543 if you have either more money, or larger machines, I would recommend
544 Oracle RDBMS. Oracle's WWW site is an excellent source of more
545 information.
546 http://www.oracle.com
548 Informix is another high-end RDBMS that is worth considering. There are
550 several differences between Oracle and Informix which are too complex
551 for this document to detail. Information on Informix can be found on
552 their WWW site at:
553 http://www.informix.com
555 In the case of WWW fronted applications, mSQL may be a better option
557 due to slow connection times between a CGI script and the Oracle RDBMS
558 and also the amount of resource each Oracle connection will consume.
559 mSQL is lighter resource-wise and faster.
560 These views are not necessarily representative of anyone else's
562 opinions, and do not reflect any corporate sponsorship or views. They
563 are provided as-is.
564 3.8 Is <insert feature here> supported in DBI?
566 Given that we're making the assumption that the feature you have
567 requested is a non-standard database-specific feature, then the answer
568 will be no.
569 DBI reflects a generic API that will work for most databases, and has
571 no database-specific functionality.
572 However, driver authors may, if they so desire, include hooks to
574 database-specific functionality through the "func()" method defined in
575 the DBI API. Script developers should note that use of functionality
576 provided via the "func()" methods is very unlikely to be portable
577 across databases.
578
580 4.1 Is DBI any use for CGI programming?
581 In a word, yes! DBI is hugely useful for CGI programming! In fact, I
582 would tentatively say that CGI programming is one of two top uses for
583 DBI.
584 DBI confers the ability to CGI programmers to power WWW-fronted
586 databases to their users, which provides users with vast quantities of
587 ordered data to play with. DBI also provides the possibility that, if a
588 site is receiving far too much traffic than their database server can
589 cope with, they can upgrade the database server behind the scenes with
590 no alterations to the CGI scripts.
591 4.2 How do I get faster connection times with DBD::Oracle and CGI?
593 Contributed by John D. Groenveld
594 The Apache "httpd" maintains a pool of "httpd" children to service
596 client requests.
597 Using the Apache mod_perl module by Doug MacEachern, the perl
599 interpreter is embedded with the "httpd" children. The CGI, DBI, and
600 your other favorite modules can be loaded at the startup of each child.
601 These modules will not be reloaded unless changed on disk.
602 For more information on Apache, see the Apache Project's WWW site:
604 http://www.apache.org
606 The mod_perl module can be downloaded from CPAN via:
608 http://www.perl.com/cgi-bin/cpan_mod?module=Apache
610 4.3 How do I get persistent connections with DBI and CGI?
612 Contributed by John D. Groenveld
613 Using Edmund Mergl's Apache::DBI module, database logins are stored in
615 a hash with each of these "httpd" child. If your application is based
616 on a single database user, this connection can be started with each
617 child. Currently, database connections cannot be shared between
618 "httpd" children.
619 Apache::DBI can be downloaded from CPAN via:
621 http://www.perl.com/cgi-bin/cpan_mod?module=Apache::DBI
623 4.4 ``When I run a perl script from the command line, it works, but, when I
625 run it under the "httpd", it fails!'' Why?
626 Basically, a good chance this is occurring is due to the fact that the
627 user that you ran it from the command line as has a correctly
628 configured set of environment variables, in the case of DBD::Oracle,
629 variables like "ORACLE_HOME", "ORACLE_SID" or "TWO_TASK".
630 The "httpd" process usually runs under the user id of "nobody", which
632 implies there is no configured environment. Any scripts attempting to
633 execute in this situation will correctly fail.
634 One way to solve this problem is to set the environment for your
636 database in a "BEGIN { }" block at the top of your script. Another
637 technique is to configure your WWW server to pass-through certain
638 environment variables to your CGI scripts.
639 Similarly, you should check your "httpd" error logfile for any clues,
641 as well as the ``Idiot's Guide To Solving Perl / CGI Problems'' and
642 ``Perl CGI Programming FAQ'' for further information. It is unlikely
643 the problem is DBI-related.
644 The ``Idiot's Guide To Solving Perl / CGI Problems'' can be located at:
646 http://www.perl.com/perl/faq/index.html
648 as can the ``Perl CGI Programming FAQ''. Read BOTH these documents
650 carefully!
651 4.5 How do I get the number of rows returned from a "SELECT" statement?
653 Count them. Read the DBI docs for the "rows()" method.
654
656 5.1 Can I do multi-threading with DBI?
657 Perl version 5.005 and later can be built to support multi-threading.
658 The DBI, as of version 1.02, does not yet support multi-threading so it
659 would be unsafe to let more than one thread enter the DBI at the same
660 time.
661 It is expected that some future version of the DBI will at least be
663 thread-safe (but not thread-hot) by automatically blocking threads
664 intering the DBI while it's already in use.
665 5.2 How do I handle BLOB data with DBI?
667 Handling BLOB data with the DBI is very straight-forward. BLOB columns
668 are specified in a SELECT statement as per normal columns. However, you
669 also need to specify a maximum BLOB size that the <I>database
670 handle</I> can fetch using the "LongReadLen" attribute.
671 For example:
673 ### $dbh is a connected database handle
675 $sth = $dbh->prepare( "SELECT blob_column FROM blobby_table" );
676 $sth->execute;
677 would fail.
679 ### $dbh is a connected database handle
681 ### Set the maximum BLOB size...
682 $dbh->{LongReadLen} = 16384; ### 16Kb...Not much of a BLOB!
683 $sth = $dbh->prepare( "..." );
685 would succeed <I>provided no column values were larger than the
687 specified value</I>.
688 If the BLOB data is longer than the value of "LongReadLen", then an
690 error will occur. However, the DBI provides an additional piece of
691 functionality that will automatically truncate the fetched BLOB to the
692 size of "LongReadLen" if it is longer. This does not cause an error to
693 occur, but may make your fetched BLOB data useless.
694 This behaviour is regulated by the "LongTruncOk" attribute which is
696 defaultly set to a false value ( thus making overlong BLOB fetches fail
697 ).
698 ### Set BLOB handling such that it's 16Kb and can be truncated
700 $dbh->{LongReadLen} = 16384;
701 $dbh->{LongTruncOk} = 1;
702 Truncation of BLOB data may not be a big deal in cases where the BLOB
704 contains run-length encoded data, but data containing checksums at the
705 end, for example, a ZIP file, would be rendered useless.
706 5.3 How can I invoke stored procedures with DBI?
708 The DBI does not define a database-independent way of calling stored
709 procedures.
710 However, most database that support them also provide a way to call
712 them from SQL statements - and the DBI certainly supports that.
713 So, assuming that you have created a stored procedure within the target
715 database, eg, an Oracle database, you can use $dbh->"do()" to
716 immediately execute the procedure. For example,
717 $dbh->do( "BEGIN someProcedure; END;" ); # Oracle-specific
719 You should also be able to "prepare" and "execute", which is the
721 recommended way if you'll be calling the procedure often.
722 5.4 How can I get return values from stored procedures with DBI?
724 Contributed by Jeff Urlwin
725 $sth = $dbh->prepare( "BEGIN foo(:1, :2, :3); END;" );
727 $sth->bind_param(1, $a);
728 $sth->bind_param_inout(2, \$path, 2000);
729 $sth->bind_param_inout(3, \$success, 2000);
730 $sth->execute;
731 Remember to perform error checking, though! ( Or use the "RaiseError"
733 attribute ).
734 5.5 How can I create or drop a database with DBI?
736 Database creation and deletion are concepts that are entirely too
737 abstract to be adequately supported by DBI. For example, Oracle does
738 not support the concept of dropping a database at all! Also, in Oracle,
739 the database server essentially is the database, whereas in mSQL, the
740 server process runs happily without any databases created in it. The
741 problem is too disparate to attack in a worthwhile way.
742 Some drivers, therefore, support database creation and deletion through
744 the private "func()" methods. You should check the documentation for
745 the drivers you are using to see if they support this mechanism.
746 5.6 How can I "commit" or "rollback" a statement with DBI?
748 See the "commit()" and "rollback()" methods in the DBI Specification.
749 Chapter 6 of "Programming the Perl DBI" discusses transaction handling
751 within the context of DBI in more detail.
752 5.7 How are "NULL" values handled by DBI?
754 "NULL" values in DBI are specified to be treated as the value "undef".
755 "NULL"s can be inserted into databases as "NULL", for example:
756 $rv = $dbh->do( "INSERT INTO table VALUES( NULL )" );
758 but when queried back, the "NULL"s should be tested against "undef".
760 This is standard across all drivers.
761 5.8 What are these "func()" methods all about?
763 The "func()" method is defined within DBI as being an entry point for
764 database-specific functionality, eg, the ability to create or drop
765 databases. Invoking these driver-specific methods is simple, for
766 example, to invoke a "createDatabase" method that has one argument, we
767 would write:
768 $rv =$dbh->func( 'argument', 'createDatabase' );
770 Software developers should note that the "func()" methods are non-
772 portable between databases.
773 5.9 Is DBI Year 2000 Compliant?
775 DBI has no knowledge of understanding of what dates are. Therefore, DBI
776 itself does not have a Year 2000 problem. Individual drivers may use
777 date handling code internally and therefore be potentially susceptible
778 to the Year 2000 problem, but this is unlikely.
779 You may also wish to read the ``Does Perl have a Year 2000 problem?''
781 section of the Perl FAQ at:
782 http://www.perl.com/CPAN/doc/FAQs/FAQ/PerlFAQ.html
784
786 The Perl5 Database Interface is FREE software. IT COMES WITHOUT
787 WARRANTY OF ANY KIND. See the DBI README for more details.
788 However, some organizations are providing either technical support or
790 training programs on DBI. The present author has no knowledge as to the
791 quality of these services. The links are included for reference
792 purposes only and should not be regarded as recommendations in any way.
793 Caveat emptor.
794 Commercial Support
796 The Perl Clinic
797 The Perl Clinic provides commercial support for Perl and Perl
798 related problems, including the DBI and its drivers. Support is
799 provided by the company with whom Tim Bunce, author of DBI and
800 DBD::Oracle, works and ActiveState. For more information on their
801 services, please see:
802 http://www.perlclinic.com
804 Training
806 Westlake Solutions
807 A hands-on class for experienced Perl CGI developers that teaches
808 how to write database-connected CGI scripts using Perl and DBI.pm.
809 This course, along with four other courses on CGI scripting with
810 Perl, is taught in Washington, DC; Arlington, Virginia; and on-site
811 worldwide upon request.
812 See:
814 http://www.westlake.com/training
816 for more details.
818
820 In this section, we present some miscellaneous WWW links that may be of
821 some interest to DBI users. These are not verified and may result in
822 unknown sites or missing documents.
823 http://www-ccs.cs.umass.edu/db.html
825 http://www.odmg.org/odmg93/updates_dbarry.html
826 http://www.jcc.com/sql_stnd.html
827
829 Alligator Descartes. Portions are Copyright their original stated
830 authors.
831
833 This document is Copyright (c)1994-2000 Alligator Descartes, with
834 portions Copyright (c)1994-2000 their original authors. This module is
835 released under the 'Artistic' license which you can find in the perl
836 distribution.
837 This document is Copyright (c)1997-2000 Alligator Descartes. All rights
839 reserved. Permission to distribute this document, in full or in part,
840 via email, Usenet, ftp archives or http is granted providing that no
841 charges are involved, reasonable attempt is made to use the most
842 current version and all credits and copyright notices are retained (
843 the AUTHOR and COPYRIGHT sections ). Requests for other distribution
844 rights, including incorporation into commercial products, such as
845 books, magazine articles or CD-ROMs should be made to Alligator
846 Descartes.
847perl v5.16.3 2013-04-04 DBI::FAQ(3)