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MAN page from RedHat Other mysql-perl-bin-3.21.23-2libc.i386.rpm

lib::DBI::FAQ

Section: User Contributed Perl Documentation (3)
Updated: perl 5.004, patch 04
Index 

NAME

DBI::FAQ -- The Frequently Asked Questions for the Perl5 Database Interface 

SYNOPSIS

    perldoc DBI::FAQ
 

VERSION

This document is currently at version 0.35, as of June 20th, 1997. 

DESCRIPTION

This document serves to answer the most frequently asked questions on boththe DBI Mailing Lists and personally to members of the DBI development team. 

Basic Information & Information Sources


1.1 What is DBI, DBperl, Oraperl and *perl?

To quote Tim Bunce, the architect and author of DBI:

    ``DBI is a database access Application Programming Interface (API)      for the Perl Language. The DBI API Specification defines a set      of functions, variables and conventions that provide a consistent      database interface independant of the actual database being used.''
In simple language, the DBI interface allows users to access multiple databasetypes transparently. So, if you connecting to an Oracle, Informix, mSQL, Sybaseor whatever database, you don't need to know the underlying mechanics of theinterface. The API defined by DBI will work on all these database types.

A similar benefit is gained by the ability to connect to two differentdatabases of different vendor within the one perl script, ie, I wantto read data from an Oracle database and insert it back into an Informixdatabase all within one program. The DBI layer allows you to do this simplyand powerfully.

DBperl is the old name for the interface specification. It's usuallynow used to denote perl4 modules on database interfacing, such as,oraperl, isqlperl, ingperl and so on. These interfacesdidn't have a standard API and are generally not supported.

Here's a list of old DBperl's, their corresponding DBI counterparts andsupport information. Please note, the author's listed here generallydo not maintain the DBI module for the same database. These emailaddresses are unverified and should only be used for queries concerning theperl4 modules listed below. DBI driver queries should be directed to thedbi-users mailing list.

  Perl4 Name  Database          Author                  DBI Driver  ----------  --------          ------                  ----------  Sybperl     Sybase            Michael Peppler         DBD::Sybase                                <mpepplerAATTitf.ch>  Oraperl     Oracle 6 & 7      Kevin Stock             DBD::Oracle                                <dbi-usersAATTfugue.com>  Ingperl     Ingres            Tim Bunce &             DBD::Ingres                                Ted Lemon                                <dbi-usersAATTfugue.com>  Interperl   Interbase         Buzz Moschetti          DBD::Interbase                                <buzzAATTbear.com>  Uniperl     Unify 5.0         Rick Wargo              None                                <rickersAATTcoe.drexel.edu>  Pgperl      Postgres          Igor Metz               DBD::Pg                                <metzAATTiam.unibe.ch>  Btreeperl   NDBM              John Conover            SDBM?                                <johnAATTjohncon.com>  Ctreeperl   C-Tree            John Conover            None                                <johnAATTjohncon.com>  Cisamperl   Informix C-ISAM   Mathias Koerber         None                                <mathiasAATTunicorn.swi.com.sg>  Duaperl     X.500 Directory   Eric Douglas            None              User Agent
However, some DBI modules have DBperl emulation layers, so, DBD::Oraclefor example comes with an Oraperl emulation layer, which allows you torun legacy oraperl scripts without modification. The emulation layertranslates the oraperl API calls into the corresponding DBI calls.

Here's a table of emulation layer information:

    Module          Emulation Layer     Status    ------          ---------------     ------    DBD::Oracle     Oraperl             Complete    DBD::Ingres     Ingperl             Complete    DBD::Informix   Isqlperl            Under development    DBD::Sybase     Sybperl             Working? ( Needs verification )    DBD::mSQL       Msqlperl            Experimentally released with                                         DBD::mSQL-0.61
The Msqlperl emulation is a special case. Msqlperl is a perl5 driverfor mSQL databases, but does not conform to the DBI Specification. It'suse is being deprecated in favour of DBD::mSQL. Msqlperl may be downloadedfrom CPAN via:

    http://www.perl.com/cgi-bin/cpan_mod?module=Msqlperl

1.2. Where can I get it from?

DBI is primarily distributed from:

    ftp://ftp.demon.co.uk/pub/perl/db
The Comprehensive Perl Archive Network resources should be used forretrieving up-to-date versions of the drivers. Local CPAN sites may beaccessed via Tom Christiansen's splendid CPAN multiplexer programlocated at:

    http://www.perl.com/CPAN/
For more specific version information and exact URLs of drivers, please seethe DBI drivers list and the DBI module pages which can be found on:

    http://www.hermetica.com/technologia/perl/DBI

1.3. Where can I get more information?

There are a few information sources on DBI.

DBI Specification

    http://www.hermetica.com/technologia/perl/DBI/doc/dbispec
There are two specifications available at this link, the new DBI DraftSpecification which is a rapidly evolving document as Tim Bunce and thedevelopment team drive towards a stable interface, and the oldhistorical DBperl Specification out of which the current DBI interfaceevolved.

The latter document should be regarded as being of historical interest only and should not serve as a programming manual, or authoratative in any sense. However, it is still a very useful reference source.

POD documentation
PODs are chunks of documentation usually embedded within perl programsthat document the code ``in place'', providing a useful resource forprogrammers and users of modules. POD for DBI and drivers is beginning to become more commonplace, and documentation for these modules can be readwith the following commands.
The DBI Specification
The POD for the DBI Specification can be read with the:

    perldoc DBI
command.
Frequently Asked Questions
This document, the Frequently Asked Questions is also available as PODdocumentation! You can read this on your own system by typing:

    perldoc DBI::FAQ
This may be more convenient to persons not permanently, or conveniently,connected to the Internet but the document may not be the latest version.
Oraperl
Users of the Oraperl emulation layer bundled with DBD::Oracle, may readup on how to program with the Oraperl interface by typing:

    perldoc Oraperl
This will produce an updated copy of the original oraperl man page written byKevin Stock for perl4. The oraperl API is fully listed and described there.
DBD::mSQL
Users of the DBD::mSQL module may read about some of the private functionsand quirks of that driver by typing:

    perldoc DBD::mSQL

POD in general
Information on writing POD, and on the philosophy of POD in general, can beread by typing:

    perldoc perlpod
Users with the Tk module installed may be interested to learn there is aTk-based POD reader available called tkpod, which formats POD in a convenientand readable way.
Rambles, Tidbits and Observations

    http://www.hermetica.com/technologia/perl/DBI/tidbits
There are a series of occasional rambles from various people on theDBI mailing lists who, in an attempt to clear up a simple point, end updrafting fairly comprehensive documents. These are quite often varying inquality, but do provide some insights into the workings of the interfaces.
``DBI -- The perl5 Database Interface''
This is an article written by Alligator Descartes and Tim Bunce on thestructure of DBI. It was published in issue 5 of ``The Perl Journal''. It's extremely good. Go buy the magazine. In fact, buy all of them! ``The Perl Journal''s WWW site is:

    http://www.tpj.com

``DBperl''
This article, published in the November 1996 edition of ``Dr. DobbsJournal'' concerned DBperl. The author of this edition apparently didnot bother to contact any of the DBI development team members for verificationof the information contained within his article. Several reviews of thearticle on the dbi-users mailing list were disparaging, to say the least.The fact the article was written about DBperl instead of DBI hintsat the staleness of the information. However, we include the referencefor completeness' sake.
``The Perl5 Database Interface''
This item is a book to be written by Alligator Descartes ( for it is me )and published by O'Reilly and Associates this coming Winter.

Here is the putative table of contents for the book.

     * Introduction          + Databases          + CGI / WWW          + perl     * Basic Database Concepts          + Types of Database               o Flat File               o AnyDBM               o RDBMS          + Using Which Database For What...     * SQL          + Why SQL?          + Structuring Information In Databases          + Retrieving Data From Databases          + Manipulating Data and Data Structures     * DBI Architecture     * Programming with DBI          + DBI Initialization          + Handles               o Driver Handles               o Database Handles               o Statement Handles          + Connection and Disconnection          + Handling Errors          + Issuing Simple Queries          + Executing Atomic Statements          + Statement MetaData          + More perl-ish Statements          + Binding          + Transaction Handling          + Utility Methods          + Handle Attributes and Dynamic Variables     * DBI and ODBC     * The Database Drivers          + DBD::Oracle and oraperl          + DBD::Informix and isqlperl          + DBD::mSQL and Msqlperl     * Case Studies          + DBI and the WWW          + Data Migration and Warehousing          + Administration Software     * Appendix: API Reference / Specification     * Appendix: Resources

README files
The README files included with each driver occasionally contains some very useful information ( no, really! ) that may be pertinent to the user.Please read them. It makes our worthless existences more bearable. Thesecan all be read from the main DBI WWW page at:

    http://www.hermetica.com/technologia/perl/DBI

Mailing Lists
There are three mailing lists for DBI run by Ted Lemon. These can allbe subscribed to and unsubscribed from via the World Wide Web at theURL of:

    http://www.fugue.com/dbi
If you cannot successfully use the WWW form on the above page, pleasesubscribe to the list in the following manner:

    Email: 'dbi-XXX-requestAATTfugue.com' with a message body of    'subscribe'
Where `dbi-XXX' is the name of the mailing list you are interested in.But note that your request will be handled by a human and may take sometime.

The lists that users may participate in are:

dbi-announce
This mailing list is for announcements only. Very low traffic. Theannouncements are usually posted on the main DBI WWW page.
dbi-dev
This mailing list is intended for the use of developers discussingideas and concepts for the DBI interface, API and driver mechanics.Only any use for developers, or interested parties. Low traffic.
dbi-users
This mailing list is a general discussion list used for bug reporting,problem discussion and general enquiries. Medium traffic.
Mailing List Archives

US Mailing List Archives

    http://outside.organic.com/mail-archives/dbi-users/
Searchable hypermail archives of the three mailing lists, and some of themuch older traffic have been set up for users to browse.
European Mailing List Archives

    http://www.rosat.mpe-garching.mpg.de/mailing-lists/PerlDB-Interest
As per the US archive above.
 

Compilation Problems


2.1. Compilation problems or It

First off, consult the online information about the module, beitDBI itself, or a DBD, and see if it's a known compilation problem on yourarchitecture. These documents can be found at:

    http://www.hermetica.com/technologia/perl/DBI
If it's a known problem, you'll probably have to wait till it gets fixed. If you're really needing it fixed, try the following:
Attempt to fix it yourself
This technique is generally not recommended to the faint-hearted.If you do think you have managed to fix it, then, send a patch file( context diff ) to the author with an explanation of:
•
What the problem was, and test cases, if possible.
•
What you needed to do to fix it. Please make sure you mention everything.
•
Platform information, database version, perl version (perl -V), moduleversion and DBI version.
Email the author Do NOT whinge!
Please email the address listed in the WWW pages for whichever driver youare having problems with. Do not directly email the author at aknown address unless it corresponds with the one listed. Some authors,including Tim Bunce, specifically do not want mail sent directly to them.

We tend to have real jobs to do, and we do read the mailing lists forproblems. Besides, we may not have access to <insert yourfavourite brain-damaged platform here> and couldn't be of anyassistance anyway! Apologies for sounding harsh, but that's the way of it!

However, you might catch one of these creative genii at 3am when we'redoing this sort of stuff anyway, and get a patch within 5 minutes. Theatmosphere in the DBI circle is that we do appreciate the users'problems, since we work in similar environments.

If you are planning to email the author, please furnish as much informationas possible, ie:

•
ALL the information asked for in the README file forthe problematic module. And we mean ALL of it. We don'tput lines like that in documentation for the good of our health, orto meet obscure README file standards of length.
•
If you have a core dump, try the Devel::CoreStack module forgenerating a stack trace from the core dump. Send us that too.Devel::CoreStack can be found on CPAN at:

    http://www.perl.com/cgi-bin/cpan_mod?module=Devel::CoreStack

•
Module versions, perl version, test cases, operating system versionsand any other pertinent information.

Remember, the more information you send us, the quicker we can track problems down. If you send us no useful information, expect nothing back.

Email the dbi-users Mailing List
It's usually a fairly intelligent idea to cc the mailing listanyway with problems. The authors all read the lists, so you lose nothingby mailing there.
 

Platform and Driver Issues


3.1 What's the difference between ODBC and DBI?

Good question! To be filled in more detail! Meanwhile see the notes at theend of the DBI README file.

3.2 Is DBI supported under Windows 95 / NT platforms?

Finally, yes! Jeff Urlwin has been working diligently on buildingDBI and DBD::Oracle under these platforms, and, with theadvent of a stabler perl and a port of MakeMaker, the project hascome on by great leaps and bounds.

Recent DBI and DBD::Oracle modules will build and work out-of-the-boxon Win32 with the standard perl 5.004 (or later) version of perl.

If you have to use the old non-standard ActiveWare perl port you can't usethe standard DBI and DBD::Oracle modules out-of-the-box. Details of the changes required and pre-patched versions can be found at:

    http://www.hermetica.com/technologia/perl/DBI/win32

3.3 Can I access Microsoft Access or SQL-Server databases with DBI?

    Contributed by Tim Bunce and Jeff Urlwin
Supplied with DBI-0.79 ( and later ) is an experimental DBI `emulation layer'for the Win32::ODBC module. It's called DBI::W32ODBC and is,at the moment, very minimal. You will need the Win32::ODBC module available from:

    http://www.roth.net
Given its status, problem reports without fixes are likely to be ignored. You will also need the Win32 DBI patch kit as supplied by Jeff Urlwin,which you can locate by reading the previous question's answer.

To get back to the question, theoretically, yes, you can access Microsoft Access and SQL-Server databases from DBI via ODBC!

3.4 Is the a DBD for <insert favourite database here>?

Is is listed on the DBI drivers page?

    http://www.hermetica.com/technologia/perl/DBI/DBD
If not, no. A complete absence of a given database driver from thatpage means that no-one has announced any intention to work on it.

A corollary of the above statement implies that if you see an announcementfor a driver not on the above page, there's a good chance it's notactually a DBI driver, and may not conform to the specifications. Therefore,questions concerning problems with that code should not really be addressedto the DBI Mailing Lists.

3.5 What's DBM? And why should I use DBI instead?

Extracted from ``DBI - The Database Interface for Perl 5'':

    ``UNIX was originally blessed with simple file-based ``databases'', namely    the dbm system. dbm lets you store data in files, and retrieve    that data quickly. However, it also has serious drawbacks.
        File Locking
        The dbm systems did not allow particularly robust file locking        capabilities, nor any capability for correcting problems arising through        simultaneous writes [ to the database ].
        Arbitrary Data Structures
        The dbm systems only allows a single fixed data structure:        key-value pairs. That value could be a complex object, such as a        [ C ] struct, but the key had to be unique. This was a large        limitation on the usefulness of dbm systems.
    However, dbm systems still provide a useful function for users with    simple datasets and limited resources, since they are fast, robust and     extremely well-tested. Perl modules to access dbm systems have now    been integrated into the core Perl distribution via the    AnyDBM_File module.''
To sum up, DBM is a perfectly satisfactory solution for essentially read-onlydatabases, or small and simple datasets with a single user. However,for more powerful and scaleable datasets, not to mention robusttransactional locking, users are recommended to use DBI.

3.6 When will mSQL-2 be supported?

As of DBD::mSQL-0.61, there has been support for mSQL-2.However, there is no real support for any of the new methods added to thecore mSQL library regarding index support yet. These are forthcomingand will be accessible via func() methods private to DBD::mSQL.You can read more about these private methods in the DBD::mSQL PODthat can be found by typing:

    perldoc DBD::mSQL
provided you have DBD::mSQL correctly installed.

3.7 What database do you recommend me using?

This is a particularly thorny area in which an objective answer is difficultto come by, since each dataset, proposed usage and system configurationdiffers from person to person.

From the current author's point of view, if the dataset is relativelysmall, being tables of less than 1 million rows, and less than 1000 tablesin a given database, then mSQL is a perfectly acceptable solutionto your problem. This database is extremely cheap, is wonderfully robustand has excellent support. More information is available on the HughesTechnology WWW site at:

    http://www.hughes.com.au
If the dataset is larger than 1 million row tables or 1000 tables, or if youhave either more money, or larger machines, I would recommend the Oracle RDBMS.Oracle's WWW site is an excellent source of more information.

    http://www.oracle.com
Informix is another high-end RDBMS that is worth considering. There areseveral differences between Oracle and Informix which are too complex forthis document to detail. Information on Informix can be found on theirWWW site at:

    http://www.informix.com
In the case of WWW fronted applications, mSQL may be a better optiondue to slow connection times between a CGI script and the Oracle RDBMS andalso the amount of resource each Oracle connection will consume. mSQLis lighter resource-wise and faster.

These views are not necessarily representative of anyone else's opinions,and do not reflect any corporate sponsorship or views. They are providedas-is.

3.8 Is <insert feature here> supported in DBI?

Given that we're making the assumption that the feature you have requestedis a non-standard database-specific feature, then the answer will be no.

DBI reflects a generic API that will work for most databases, and hasno database-specific functionality defined.

However, driver authors may, if they so desire, include hooks to database-specificfunctionality through the func() method defined in the DBI API.Script developers should note that use of functionality provided viathe func() methods is unlikely to be portable across databases. 

Programming Questions


4.1 Is DBI any use for CGI programming?

In a word, yes! DBI is hugely useful for CGI programming! In fact, I wouldtentatively say that CGI programming is one of two top uses for DBI.

DBI confers the ability to CGI programmers to power WWW-fronted databasesto their users, which provides users with vast quantities of ordereddata to play with. DBI also provides the possibility that, if a site isreceiving far too much traffic than their database server can cope with, theycan upgrade the database server behind the scenes with no alterations tothe CGI scripts.

4.2 How do I get faster connection times with DBD::Oracle and CGI?

    Contributed by John D. Groenveld
The Apache httpd maintains a pool of httpd children to service client requests.

Using the Apache mod_perl module by Doug MacEachern, the perl interpreter is embedded with the httpd children. The CGI, DBI, and your other favorite modules can be loaded at the startup of each child. These modules will not be reloaded unless changed on disk.

For more information on Apache, see the Apache Project's WWW site:

    http://www.apache.org/
The mod_perl module can be downloaded from CPAN via:

    http://www.perl.com/cgi-bin/cpan_mod?module=Apache

4.3 How do I get persistent connections with DBI and CGI?

    Contributed by John D. Groenveld
Using Edmund Mergl's Apache::DBI module, database logins are stored in a hash with each of these httpd child. If your application is based on a single database user, this connection can be started with each child. Currently, database connections cannot be shared between httpd children.

Apache::DBI can be downloaded from CPAN via:

    http://www.perl.com/cgi-bin/cpan_mod?module=Apache::DBI

4.4 ``My perl script runs from the command line, but fails under the httpd!'' Why?

Basically, a good chance this is occurring is due to the fact that the userthat you ran it from the command line as has a correctly configured set ofenvironment variables, in the case of DBD::Oracle, variables like$ORACLE_HOME, $ORACLE_SID or TWO_TASK.

The httpd process usually runs under the user id of nobody,which implies there is no configured environment. Any scripts attempting toexecute in this situation will correctly fail.

To solve this problem, set the environment for your database in a BEGIN { }block at the top of your script. This will generally solve the problem.

Similarly, you should check your httpd error logfile for any clues, aswell as the very valuable ``Idiot's Guide To Solving Perl / CGI Problems''and ``Perl CGI Programming FAQ'' for further information. It isunlikely the problem is DBI-related.

The ``Idiot's Guide To Solving Perl / CGI Problems'' can be located at:

    http://www.perl.com/perl/faq/index.html
as can the ``Perl CGI Programming FAQ''. Read BOTH these documents carefully! They will probably save you many hours of work.

5.1 Can I do multi-threading with DBI?

As of the current date of this FAQ ( see top of page ), no. perldoes not support multi-threading. However, multi-threading is expected tobecome part of the perl core distribution as of version 5.005, which impliesthat DBI may support multi-threading fairly soon afterwards.

For some OCI example code for Oracle that has multi-threaded SELECTstatements, see:

    http://www.hermetica.com/technologia/oracle/oci/orathreads.tar.gz

5.2 How do I handle BLOB data with DBI?

To be written.

5.3 How can I invoke stored procedures with DBI?

There is currently no standard way to call stored procedures with DBI.However, if the database lets you use SQL to call stored proceduresthen the DBI and DBD driver probably will to.

For example, assuming that you have created a stored procedure withinan Oracle database, you can use $dbh->do() to immediately executethe procedure:

    $dbh->do( "BEGIN someProcedure END;" );     # Oracle specific

5.4 How can I get return values from stored procedures with DBI?

    Note: This is Oracle specific. Contributed by Jeff Urlwin
    $sth = $dbh->prepare( "BEGIN foo(:1, :2, :3); END;" )  # Oracle specific               || die $sth->errstr;    $sth->bind_param(1, $a) || die $sth->errstr;    $sth->bind_param_inout(2, \$path, 2000)    || die $sth->errstr;    $sth->bind_param_inout(3, \$success, 2000) || die $sth->errstr;    $sth->execute || die $sth->errstr;
Note the error checking, it may seem like extra work but it'll probably saveyou hours in the long run. See $sth->{RaiseError} and $sth->{printError}in the DBI docs for easier ways to get the same effect.

5.5 How can I create or drop a database with DBI?

Database creation and deletion are concepts that are too abstractto be adequately supported by DBI. For example, Oracle does not support theconcept of dropping a database at all! Also, in Oracle, the databaseserver essentially is the database, whereas in mSQL, theserver process runs happily without any databases created in it. Theproblem is too disparate to attack easily.

Some drivers, therefore, support database creation and deletion throughthe private func() methods. You should check the documentation forthe drivers you are using to see if they support this mechanism.

5.6 How can I commit or rollback a statement with DBI?

To be written. See the commit or rollback methods in the DBI docs.

5.7 How are NULL values handled by DBI?

NULL values in DBI are specified to be treated as the value undef.NULLs can be inserted into databases as NULL, for example:

    $rv = $dbh->do( "INSERT INTO table VALUES( NULL )" );
but when queried back, the NULLs should be tested against undef.This is standard across all drivers.

5.8 What are these func() methods all about?

The func() method is defined within DBI as being an entry pointfor database-specific functionality, eg, the ability to create ordrop databases. Invoking these driver-specific methods is simple, for example,to invoke a createDatabase method that has one argument, we wouldwrite:

    $rv = $dbh->func( 'argument', 'createDatabase' );
Software developers should note that the func() methods arenon-portable between databases. 

Support and Training

The Perl5 Database Interface is FREE software. IT COMES WITHOUT WARRANTYOF ANY KIND. See the DBI README and DBI documentation for more details.

However, some organizations are providing either technical support ortraining programs on DBI. The present author has no knowledge asto the quality of these services. The links are included for referencepurposes only.

Commercial Support


The Perl Clinic
The Perl Clinic can arrange commercial support contracts for Perl, DBI,DBD::Oracle and Oraperl. Support is provided by the company with whomTim Bunce, author of DBI and DBD::Oracle, works. For more informationon their services, please see:

    http://www.perl.co.uk/tpc
for more details.

Training

No training programs are known at this time. 

Other References

In this section, we present some miscellaneous WWW links that may be ofsome interest to DBI users. These are not verified and may result inunknown sites or missing documents.

    http://www-ccs.cs.umass.edu/db.html    http://www.odmg.org/odmg93/updates_dbarry.html    http://www.jcc.com/sql_stnd.html
 

AUTHOR

Alligator Descartes <descarteAATThermetica.com> 

COPYRIGHT

This document is Copyright (c)1994-1997 Alligator Descartes, with portionsCopyright (c)1994-1997 their original authors. This module is released underthe `Artistic' license which you can find in the perl distribution.

This document is Copyright (c)1997 Alligator Descartes. All rights reserved.Permission to distribute this document, in full or in part, via email,Usenet, ftp archives or http is granted providing that no charges are involved,reasonable attempt is made to use the most current version and all creditsand copyright notices are retained ( the AUTHOR and COPYRIGHT sections ).Requests for other distribution rights, including incorporation into commercial products, such as books, magazine articles or CD-ROMs should bemade to Alligator Descartes <descarteAATThermetica.com>.

 

Index

NAME
SYNOPSIS
VERSION
DESCRIPTION
Basic Information & Information Sources
Compilation Problems
Platform and Driver Issues
Programming Questions
Support and Training
Other References
AUTHOR
COPYRIGHT
This document was created byman2html,using the manual pages.
  
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