Edit File: DBI::FAQ.3pm
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" DBI::FAQ \-\- The Frequently Asked Questions for the Perl5 Database Interface .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& perldoc DBI::FAQ .Ve .SH "VERSION" .IX Header "VERSION" This document is currently at version \fI0.38\fR, as of \fIFebruary 8th, 2000\fR. .PP That's \fBvery\fR old. A newer \s-1FAQ\s0 can be found at <http://faq.dbi\-support.com/> .PP Neither this document nor that web site are actively maintained. Volunteers are welcome. .SH "DESCRIPTION" .IX Header "DESCRIPTION" This document serves to answer the most frequently asked questions on both the \s-1DBI\s0 Mailing Lists and personally to members of the \s-1DBI\s0 development team. .SH "Basic Information & Information Sources" .IX Header "Basic Information & Information Sources" .SS "1.1 What is \s-1DBI\s0, DBperl, Oraperl and *perl?" .IX Subsection "1.1 What is DBI, DBperl, Oraperl and *perl?" To quote Tim Bunce, the architect and author of \s-1DBI:\s0 .PP .Vb 4 \& 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 independent of the actual database being used. .Ve .PP In simple language, the \s-1DBI\s0 interface allows users to access multiple database types transparently. So, if you connecting to an Oracle, Informix, mSQL, Sybase or whatever database, you don't need to know the underlying mechanics of the 3GL layer. The \s-1API\s0 defined by \s-1DBI\s0 will work on \fIall\fR these database types. .PP A similar benefit is gained by the ability to connect to two \fIdifferent\fR databases of different vendor within the one perl script, \fIie\fR, I want to read data from an Oracle database and insert it back into an Informix database all within one program. The \s-1DBI\s0 layer allows you to do this simply and powerfully. .PP \&\fIDBperl\fR is the old name for the interface specification. It's usually now used to denote perl\fI4\fR modules on database interfacing, such as, \&\fIoraperl\fR, \fIisqlperl\fR, \fIingperl\fR and so on. These interfaces didn't have a standard \s-1API\s0 and are generally \fInot\fR supported. .PP Here's a list of DBperl modules, their corresponding \s-1DBI\s0 counterparts and support information. \fIPlease note\fR, the author's listed here generally \&\fIdo not\fR maintain the \s-1DBI\s0 module for the same database. These email addresses are unverified and should only be used for queries concerning the perl4 modules listed below. \s-1DBI\s0 driver queries should be directed to the \&\fIdbi-users\fR mailing list. .PP .Vb 10 \& Module Name Database Required Author DBI \& \-\-\-\-\-\-\-\-\-\-\- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- \-\-\-\-\-\- \-\-\- \& Sybperl Sybase Michael Peppler DBD::Sybase \& <mpeppler@itf.ch> \& Oraperl Oracle 6 & 7 Kevin Stock DBD::Oracle \& <dbi\-users@perl.org> \& Ingperl Ingres Tim Bunce & DBD::Ingres \& Ted Lemon \& <dbi\-users@perl.org> \& Interperl Interbase Buzz Moschetti DBD::Interbase \& <buzz@bear.com> \& Uniperl Unify 5.0 Rick Wargo None \& <rickers@coe.drexel.edu> \& Pgperl Postgres Igor Metz DBD::Pg \& <metz@iam.unibe.ch> \& Btreeperl NDBM John Conover SDBM? \& <john@johncon.com> \& Ctreeperl C\-Tree John Conover None \& <john@johncon.com> \& Cisamperl Informix C\-ISAM Mathias Koerber None \& <mathias@unicorn.swi.com.sg> \& Duaperl X.500 Directory Eric Douglas None \& User Agent .Ve .PP However, some \s-1DBI\s0 modules have DBperl emulation layers, so, \fIDBD::Oracle\fR comes with an Oraperl emulation layer, which allows you to run legacy oraperl scripts without modification. The emulation layer translates the oraperl \s-1API\s0 calls into \s-1DBI\s0 calls and executes them through the \s-1DBI\s0 switch. .PP Here's a table of emulation layer information: .PP .Vb 8 \& Module Emulation Layer Status \& \-\-\-\-\-\- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\- \-\-\-\-\-\- \& DBD::Oracle Oraperl Complete \& DBD::Informix Isqlperl Under development \& DBD::Ingres Ingperl Complete? \& DBD::Sybase Sybperl Working? ( Needs verification ) \& DBD::mSQL Msqlperl Experimentally released with \& DBD::mSQL\-0.61 .Ve .PP The \fIMsqlperl\fR emulation is a special case. \fIMsqlperl\fR is a perl5 driver for \fImSQL\fR databases, but does not conform to the \s-1DBI\s0 Specification. It's use is being deprecated in favour of \fIDBD::mSQL\fR. \fIMsqlperl\fR may be downloaded from \s-1CPAN\s0 \fIvia\fR: .PP .Vb 1 \& http://www.perl.com/cgi\-bin/cpan_mod?module=Msqlperl .Ve .SS "1.2. Where can I get it from?" .IX Subsection "1.2. Where can I get it from?" The Comprehensive Perl Archive Network resources should be used for retrieving up-to-date versions of the \s-1DBI\s0 and drivers. \s-1CPAN\s0 may be accessed \fIvia\fR Tom Christiansen's splendid \&\fI\s-1CPAN\s0 multiplexer\fR program located at: .PP .Vb 1 \& http://www.perl.com/CPAN/ .Ve .PP For more specific version information and exact URLs of drivers, please see the \s-1DBI\s0 drivers list and the \s-1DBI\s0 module pages which can be found on: .PP .Vb 1 \& http://dbi.perl.org/ .Ve .PP This list is automatically generated on a nightly basis from \s-1CPAN\s0 and should be up-to-date. .SS "1.3. Where can I get more information?" .IX Subsection "1.3. Where can I get more information?" There are a few information sources on \s-1DBI\s0. .ie n .IP "\fI""Programming the Perl \s-1DBI\s0""\fR" 4 .el .IP "\fI``Programming the Perl \s-1DBI\s0''\fR" 4 .IX Item "Programming the Perl DBI" \&\*(L"Programming the Perl \s-1DBI\s0\*(R" is the \fIofficial\fR book on the \s-1DBI\s0 written by Alligator Descartes and Tim Bunce and published by O'Reilly & Associates. The book was released on February 9th, 2000. .Sp The table of contents is: .Sp .Vb 10 \& Preface \& 1. Introduction \& From Mainframes to Workstations \& Perl \& DBI in the Real World \& A Historical Interlude and Standing Stones \& 2. Basic Non\-DBI Databases \& Storage Managers and Layers \& Query Languages and Data Functions \& Standing Stones and the Sample Database \& Flat\-File Databases \& Putting Complex Data into Flat Files \& Concurrent Database Access and Locking \& DBM Files and the Berkeley Database Manager \& The MLDBM Module \& Summary \& 3. SQL and Relational Databases \& The Relational Database Methodology \& Datatypes and NULL Values \& Querying Data \& Modifying Data Within Tables \& Creating and Destroying Tables \& 4. Programming with the DBI \& DBI Architecture \& Handles \& Data Source Names \& Connection and Disconnection \& Error Handling \& Utility Methods and Functions \& 5. Interacting with the Database \& Issuing Simple Queries \& Executing Non\-SELECT Statements \& Binding Parameters to Statements \& Binding Output Columns \& do() Versus prepare() \& Atomic and Batch Fetching \& 6. Advanced DBI \& Handle Attributes and Metadata \& Handling LONG/LOB Data \& Transactions, Locking, and Isolation \& 7. ODBC and the DBI \& ODBC \-\- Embraced and Extended \& DBI \-\- Thrashed and Mutated \& The Nuts and Bolts of ODBC \& ODBC from Perl \& The Marriage of DBI and ODBC \& Questions and Choices \& Moving Between Win32::ODBC and the DBI \& And What About ADO? \& 8. DBI Shell and Database Proxying \& dbish \-\- The DBI Shell \& Database Proxying \& A. DBI Specification \& B. Driver and Database Characteristics \& C. ASLaN Sacred Site Charter \& Index .Ve .Sp The book should be available from all good bookshops and can be ordered online either <I>via</I> O'Reilly & Associates .Sp .Vb 1 \& http://www.oreilly.com/catalog/perldbi .Ve .Sp or Amazon .Sp .Vb 1 \& http://www.amazon.com/exec/obidos/ASIN/1565926994/dbi .Ve .IP "\fI\s-1POD\s0 documentation\fR" 4 .IX Item "POD documentation" \&\fI\s-1POD\s0\fRs are chunks of documentation usually embedded within perl programs that document the code ``\fIin place\fR'', providing a useful resource for programmers and users of modules. \s-1POD\s0 for \s-1DBI\s0 and drivers is beginning to become more commonplace, and documentation for these modules can be read with the \f(CW\*(C`perldoc\*(C'\fR program included with Perl. .RS 4 .IP "The \s-1DBI\s0 Specification" 4 .IX Item "The DBI Specification" The \s-1POD\s0 for the \s-1DBI\s0 Specification can be read with the: .Sp .Vb 1 \& perldoc DBI .Ve .Sp command. The Specification also forms Appendix A of \*(L"Programming the Perl \&\s-1DBI\s0\*(R". .IP "Oraperl" 4 .IX Item "Oraperl" Users of the Oraperl emulation layer bundled with \fIDBD::Oracle\fR, may read up on how to program with the Oraperl interface by typing: .Sp .Vb 1 \& perldoc Oraperl .Ve .Sp This will produce an updated copy of the original oraperl man page written by Kevin Stock for perl4. The oraperl \s-1API\s0 is fully listed and described there. .IP "Drivers" 4 .IX Item "Drivers" Users of the \s-1DBD\s0 modules may read about some of the private functions and quirks of that driver by typing: .Sp .Vb 1 \& perldoc <driver> .Ve .Sp For example, the \fIDBD::mSQL\fR driver is bundled with driver-specific documentation that can be accessed by typing .Sp .Vb 1 \& perldoc DBD::mSQL .Ve .IP "Frequently Asked Questions" 4 .IX Item "Frequently Asked Questions" This document, the \fIFrequently Asked Questions\fR is also available as \s-1POD\s0 documentation! You can read this on your own system by typing: .Sp .Vb 1 \& perldoc DBI::FAQ .Ve .Sp This may be more convenient to persons not permanently, or conveniently, connected to the Internet. The \fI\s-1DBI::FAQ\s0\fR module should be downloaded and installed for the more up-to-date version. .Sp The version of \fI\s-1DBI::FAQ\s0\fR shipped with the \f(CW\*(C`DBI\*(C'\fR module may be slightly out of date. .IP "\s-1POD\s0 in general" 4 .IX Item "POD in general" Information on writing \s-1POD\s0, and on the philosophy of \s-1POD\s0 in general, can be read by typing: .Sp .Vb 1 \& perldoc perlpod .Ve .Sp Users with the Tk module installed may be interested to learn there is a Tk-based \s-1POD\s0 reader available called \f(CW\*(C`tkpod\*(C'\fR, which formats \s-1POD\s0 in a convenient and readable way. This is available \fIvia\fR \s-1CPAN\s0 as the module called \&\fITk::POD\fR and is highly recommended. .RE .RS 4 .RE .IP "\fIDriver and Database Characteristics\fR" 4 .IX Item "Driver and Database Characteristics" The driver summaries that were produced for Appendix B of \*(L"Programming the Perl \s-1DBI\s0\*(R" are available online at: .Sp .Vb 1 \& http://dbi.perl.org/ .Ve .Sp in the driver information table. These summaries contain standardised information on each driver and database which should aid you in selecting a database to use. It will also inform you quickly of any issues within drivers or whether a driver is not fully compliant with the \s-1DBI\s0 Specification. .IP "\fIRambles, Tidbits and Observations\fR" 4 .IX Item "Rambles, Tidbits and Observations" .Vb 1 \& http://dbi.perl.org/tidbits .Ve .Sp There are a series of occasional rambles from various people on the \&\s-1DBI\s0 mailing lists who, in an attempt to clear up a simple point, end up drafting fairly comprehensive documents. These are quite often varying in quality, but do provide some insights into the workings of the interfaces. .IP "\fIArticles\fR" 4 .IX Item "Articles" A list of articles discussing the \s-1DBI\s0 can be found on the \s-1DBI\s0 \s-1WWW\s0 page at: .Sp .Vb 1 \& http://dbi.perl.org/ .Ve .Sp These articles are of varying quality and age, from the original Perl Journal article written by Alligator and Tim, to more recent debacles published online from about.com. .IP "\fI\s-1README\s0 files\fR" 4 .IX Item "README files" The \fI\s-1README\s0\fR files included with each driver occasionally contains some useful information ( no, really! ) that may be pertinent to the user. Please read them. It makes our worthless existences more bearable. These can all be read from the main \s-1DBI\s0 \s-1WWW\s0 page at: .Sp .Vb 1 \& http://dbi.perl.org/ .Ve .IP "\fIMailing Lists\fR" 4 .IX Item "Mailing Lists" There are three mailing lists for \s-1DBI:\s0 .Sp .Vb 3 \& dbi\-announce@perl.org \-\- for announcements, very low traffic \& dbi\-users@perl.org \-\- general user support \& dbi\-dev@perl.org \-\- for driver developers (no user support) .Ve .Sp For information on how to subscribe, set digest mode etc, and unsubscribe, send an email message (the content will be ignored) to: .Sp .Vb 3 \& dbi\-announce\-help@perl.org \& dbi\-users\-help@perl.org \& dbi\-dev\-help@perl.org .Ve .IP "\fIMailing List Archives\fR" 4 .IX Item "Mailing List Archives" .RS 4 .PD 0 .IP "\fI\s-1US\s0 Mailing List Archives\fR" 4 .IX Item "US Mailing List Archives" .PD .Vb 1 \& http://outside.organic.com/mail\-archives/dbi\-users/ .Ve .Sp Searchable hypermail archives of the three mailing lists, and some of the much older traffic have been set up for users to browse. .IP "\fIEuropean Mailing List Archives\fR" 4 .IX Item "European Mailing List Archives" .Vb 1 \& http://www.rosat.mpe\-garching.mpg.de/mailing\-lists/PerlDB\-Interest .Ve .Sp As per the \s-1US\s0 archive above. .RE .RS 4 .RE .SH "Compilation Problems" .IX Header "Compilation Problems" .ie n .SS "2.1. Compilation problems or ""It fails the test!""" .el .SS "2.1. Compilation problems or ``It fails the test!''" .IX Subsection "2.1. Compilation problems or It fails the test!" First off, consult the \s-1README\s0 for that driver in case there is useful information about the problem. It may be a known problem for your given architecture and operating system or database. You can check the \s-1README\s0 files for each driver in advance online at: .PP .Vb 1 \& http://dbi.perl.org/ .Ve .PP If it's a known problem, you'll probably have to wait till it gets fixed. If you're \fIreally\fR needing it fixed, try the following: .IP "\fIAttempt to fix it yourself\fR" 4 .IX Item "Attempt to fix it yourself" This technique is generally \fInot\fR 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: .RS 4 .IP "\(bu" 4 What the problem was, and test cases, if possible. .IP "\(bu" 4 What you needed to do to fix it. Please make sure you mention everything. .IP "\(bu" 4 Platform information, database version, perl version, module version and \&\s-1DBI\s0 version. .RE .RS 4 .RE .IP "\fIEmail the author\fR Do \fI\s-1NOT\s0\fR whinge!" 4 .IX Item "Email the author Do NOT whinge!" Please email the address listed in the \s-1WWW\s0 pages for whichever driver you are having problems with. Do \fInot\fR directly email the author at a known address unless it corresponds with the one listed. .Sp We tend to have real jobs to do, and we do read the mailing lists for problems. Besides, we may not have access to <\fIinsert your favourite brain-damaged platform here\fR> and couldn't be of any assistance anyway! Apologies for sounding harsh, but that's the way of it! .Sp However, you might catch one of these creative genii at 3am when we're doing this sort of stuff anyway, and get a patch within 5 minutes. The atmosphere in the \s-1DBI\s0 circle is that we \fIdo\fR appreciate the users' problems, since we work in similar environments. .Sp If you are planning to email the author, please furnish as much information as possible, \fIie\fR: .RS 4 .IP "\(bu" 4 \&\fI\s-1ALL\s0\fR the information asked for in the \s-1README\s0 file in the problematic module. And we mean \fI\s-1ALL\s0\fR of it. We don't put lines like that in documentation for the good of our health, or to meet obscure \s-1README\s0 file standards of length. .IP "\(bu" 4 If you have a core dump, try the \fIDevel::CoreStack\fR module for generating a stack trace from the core dump. Send us that too. \&\fIDevel::CoreStack\fR can be found on \s-1CPAN\s0 at: .Sp .Vb 1 \& http://www.perl.com/cgi\-bin/cpan_mod?module=Devel::CoreStack .Ve .IP "\(bu" 4 Module versions, perl version, test cases, operating system versions and \fIany other pertinent information\fR. .RE .RS 4 .Sp Remember, the more information you send us, the quicker we can track problems down. If you send us no useful information, expect nothing back. .Sp Finally, please be aware that some authors, including Tim Bunce, specifically request that you do \fInot\fR mail them directly. Please respect their wishes and use the email addresses listed in the appropriate module \f(CW\*(C`README\*(C'\fR file. .RE .IP "\fIEmail the dbi-users Mailing List\fR" 4 .IX Item "Email the dbi-users Mailing List" It's usually a fairly intelligent idea to \fIcc\fR the mailing list anyway with problems. The authors all read the lists, so you lose nothing by mailing there. .SH "Platform and Driver Issues" .IX Header "Platform and Driver Issues" .SS "3.1 What's the difference between \s-1ODBC\s0 and \s-1DBI\s0?" .IX Subsection "3.1 What's the difference between ODBC and DBI?" In terms of architecture \- not much: Both define programming interfaces. Both allow multiple drivers to be loaded to do the actual work. .PP In terms of ease of use \- much: The \s-1DBI\s0 is a 'high level' interface that, like Perl itself, strives to make the simple things easy while still making the hard things possible. The \s-1ODBC\s0 is a 'low level' interface. All nuts-bolts-knobs-and-dials. .PP Now there's an \s-1ODBC\s0 driver for the \s-1DBI\s0 (\s-1DBD::ODBC\s0) the \*(L"What's the difference\*(R" question is more usefully rephrased as: .PP Chapter 7 of \*(L"Programming the Perl \s-1DBI\s0\*(R" covers this topic in far more detail and should be consulted. .SS "3.2 What's the difference between Win32::ODBC and \s-1DBD::ODBC\s0?" .IX Subsection "3.2 What's the difference between Win32::ODBC and DBD::ODBC?" The \s-1DBI\s0, and thus \s-1DBD::ODBC\s0, has a different philosophy from the Win32::ODBC module: .PP The Win32::ODBC module is a 'thin' layer over the low-level \s-1ODBC\s0 \s-1API\s0. The \s-1DBI\s0 defines a simpler 'higher level' interface. .PP The Win32::ODBC module gives you access to more of the \s-1ODBC\s0 \s-1API\s0. The \s-1DBI\s0 and \s-1DBD::ODBC\s0 give you access to only the essentials. (But, unlike Win32::ODBC, the \s-1DBI\s0 and \s-1DBD::ODBC\s0 do support parameter binding and multiple prepared statements which reduces the load on the database server and can dramatically increase performance.) .PP The Win32::ODBC module only works on Win32 systems. The \s-1DBI\s0 and \s-1DBD::ODBC\s0 are very portable and work on Win32 and Unix. .PP The \s-1DBI\s0 and \s-1DBD::ODBC\s0 modules are supplied as a standard part of the Perl 5.004 binary distribution for Win32 (they don't work with the older, non-standard, ActiveState port). .PP Scripts written with the \s-1DBI\s0 and \s-1DBD::ODBC\s0 are faster than Win32::ODBC on Win32 and are trivially portable to other supported database types. .PP The \s-1DBI\s0 offers optional automatic printing or \fIdie()\fRing on errors which makes applications simpler and more robust. .PP The current \s-1DBD::ODBC\s0 driver version 0.16 is new and not yet fully stable. A new release is due soon [relative to the date of the next \s-1TPJ\s0 issue :\-] and will be much improved and offer more \s-1ODBC\s0 functionality. .PP To summarise: The Win32::ODBC module is your best choice if you need access to more of the \s-1ODBC\s0 \s-1API\s0 than the \s-1DBI\s0 gives you. Otherwise, the \&\s-1DBI\s0 and \s-1DBD::ODBC\s0 combination may be your best bet. .PP Chapter 7 of \*(L"Programming the Perl \s-1DBI\s0\*(R" covers this topic in far more detail and should be consulted. .SS "3.3 Is \s-1DBI\s0 supported under Windows 95 / \s-1NT\s0 platforms?" .IX Subsection "3.3 Is DBI supported under Windows 95 / NT platforms?" Finally, yes! Jeff Urlwin has been working diligently on building \&\fI\s-1DBI\s0\fR and \fI\s-1DBD::ODBC\s0\fR under these platforms, and, with the advent of a stabler perl and a port of \fIMakeMaker\fR, the project has come on by great leaps and bounds. .PP The \fI\s-1DBI\s0\fR and \fIDBD::Oracle\fR Win32 ports are now a standard part of \s-1DBI\s0, so, downloading \fI\s-1DBI\s0\fR of version higher than \fI0.81\fR should work fine as should using the most recent \fIDBD::Oracle\fR version. .SS "3.4 Can I access Microsoft Access or SQL-Server databases with \s-1DBI\s0?" .IX Subsection "3.4 Can I access Microsoft Access or SQL-Server databases with DBI?" Yes, use the \fI\s-1DBD::ODBC\s0\fR driver. .SS "3.5 Is there a \s-1DBD\s0 for <\fIinsert favourite database here\fP>?" .IX Subsection "3.5 Is there a DBD for <insert favourite database here>?" First check if a driver is available on \s-1CPAN\s0 by searching for the name of the database (including common abbreviations and aliases). .PP Here's a general query that'll match all distributions: .PP .Vb 1 \& http://search.cpan.org/search?query=DBD&mode=dist .Ve .PP If you can't find a driver that way, you could check if the database supports \&\s-1ODBC\s0 drivers. If so then you could probably use the \s-1DBD::ODBC\s0 driver: .PP .Vb 1 \& http://search.cpan.org/dist/DBD\-ODBC/ .Ve .PP If not, then try asking on the dbi-users mailing list. .SS "3.6 What's \s-1DBM\s0? And why should I use \s-1DBI\s0 instead?" .IX Subsection "3.6 What's DBM? And why should I use DBI instead?" Extracted from ``\fI\s-1DBI\s0 \- The Database Interface for Perl 5\fR'': .PP .Vb 3 \& \`\`UNIX was originally blessed with simple file\-based \`\`databases\*(Aq\*(Aq, 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.\*(Aq\*(Aq .Ve .PP To sum up, \s-1DBM\s0 is a perfectly satisfactory solution for essentially read-only databases, or small and simple datasets. However, for more scalable dataset handling, not to mention robust transactional locking, users are recommended to use a more powerful database engine \fIvia\fR \fI\s-1DBI\s0\fR. .PP Chapter 2 of \*(L"Programming the Perl \s-1DBI\s0\*(R" discusses \s-1DBM\s0 files in detail. .SS "3.7 What database do you recommend me using?" .IX Subsection "3.7 What database do you recommend me using?" This is a particularly thorny area in which an objective answer is difficult to come by, since each dataset, proposed usage and system configuration differs from person to person. .PP From the current author's point of view, if the dataset is relatively small, being tables of less than 1 million rows, and less than 1000 tables in a given database, then \fImSQL\fR is a perfectly acceptable solution to your problem. This database is extremely cheap, is wonderfully robust and has excellent support. More information is available on the Hughes Technology \s-1WWW\s0 site at: .PP .Vb 1 \& http://www.hughes.com.au .Ve .PP You may also wish to look at MySQL which is a more powerful database engine that has a similar feel to mSQL. .PP .Vb 1 \& http://www.tcx.se .Ve .PP If the dataset is larger than 1 million row tables or 1000 tables, or if you have either more money, or larger machines, I would recommend \fIOracle \s-1RDBMS\s0\fR. Oracle's \s-1WWW\s0 site is an excellent source of more information. .PP .Vb 1 \& http://www.oracle.com .Ve .PP \&\fIInformix\fR is another high-end \s-1RDBMS\s0 that is worth considering. There are several differences between Oracle and Informix which are too complex for this document to detail. Information on Informix can be found on their \&\s-1WWW\s0 site at: .PP .Vb 1 \& http://www.informix.com .Ve .PP In the case of \s-1WWW\s0 fronted applications, \fImSQL\fR may be a better option due to slow connection times between a \s-1CGI\s0 script and the Oracle \s-1RDBMS\s0 and also the amount of resource each Oracle connection will consume. \fImSQL\fR is lighter resource-wise and faster. .PP These views are not necessarily representative of anyone else's opinions, and do not reflect any corporate sponsorship or views. They are provided \&\fIas-is\fR. .SS "3.8 Is <\fIinsert feature here\fP> supported in \s-1DBI\s0?" .IX Subsection "3.8 Is <insert feature here> supported in DBI?" Given that we're making the assumption that the feature you have requested is a non-standard database-specific feature, then the answer will be \fIno\fR. .PP \&\s-1DBI\s0 reflects a \fIgeneric\fR \s-1API\s0 that will work for most databases, and has no database-specific functionality. .PP However, driver authors may, if they so desire, include hooks to database-specific functionality through the \f(CW\*(C`func()\*(C'\fR method defined in the \s-1DBI\s0 \s-1API\s0. Script developers should note that use of functionality provided \fIvia\fR the \f(CW\*(C`func()\*(C'\fR methods is very unlikely to be portable across databases. .SH "Programming Questions" .IX Header "Programming Questions" .SS "4.1 Is \s-1DBI\s0 any use for \s-1CGI\s0 programming?" .IX Subsection "4.1 Is DBI any use for CGI programming?" In a word, yes! \s-1DBI\s0 is hugely useful for \s-1CGI\s0 programming! In fact, I would tentatively say that \s-1CGI\s0 programming is one of two top uses for \s-1DBI\s0. .PP \&\s-1DBI\s0 confers the ability to \s-1CGI\s0 programmers to power WWW-fronted databases to their users, which provides users with vast quantities of ordered data to play with. \s-1DBI\s0 also provides the possibility that, if a site is receiving far too much traffic than their database server can cope with, they can upgrade the database server behind the scenes with no alterations to the \s-1CGI\s0 scripts. .SS "4.2 How do I get faster connection times with DBD::Oracle and \s-1CGI\s0?" .IX Subsection "4.2 How do I get faster connection times with DBD::Oracle and CGI?" .Vb 1 \& Contributed by John D. Groenveld .Ve .PP The Apache \f(CW\*(C`httpd\*(C'\fR maintains a pool of \f(CW\*(C`httpd\*(C'\fR children to service client requests. .PP Using the Apache \fImod_perl\fR module by \fIDoug MacEachern\fR, the perl interpreter is embedded with the \f(CW\*(C`httpd\*(C'\fR children. The \s-1CGI\s0, \s-1DBI\s0, and your other favorite modules can be loaded at the startup of each child. These modules will not be reloaded unless changed on disk. .PP For more information on Apache, see the Apache Project's \s-1WWW\s0 site: .PP .Vb 1 \& http://www.apache.org .Ve .PP The \fImod_perl\fR module can be downloaded from \s-1CPAN\s0 \fIvia\fR: .PP .Vb 1 \& http://www.perl.com/cgi\-bin/cpan_mod?module=Apache .Ve .SS "4.3 How do I get persistent connections with \s-1DBI\s0 and \s-1CGI\s0?" .IX Subsection "4.3 How do I get persistent connections with DBI and CGI?" .Vb 1 \& Contributed by John D. Groenveld .Ve .PP Using Edmund Mergl's \fIApache::DBI\fR module, database logins are stored in a hash with each of these \f(CW\*(C`httpd\*(C'\fR 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 \f(CW\*(C`httpd\*(C'\fR children. .PP \&\fIApache::DBI\fR can be downloaded from \s-1CPAN\s0 \fIvia\fR: .PP .Vb 1 \& http://www.perl.com/cgi\-bin/cpan_mod?module=Apache::DBI .Ve .ie n .SS "4.4 ``When I run a perl script from the command line, it works, but, when I run it under the ""httpd"", it fails!'' Why?" .el .SS "4.4 ``When I run a perl script from the command line, it works, but, when I run it under the \f(CWhttpd\fP, it fails!'' Why?" .IX Subsection "4.4 ``When I run a perl script from the command line, it works, but, when I run it under the httpd, it fails!'' Why?" Basically, a good chance this is occurring is due to the fact that the user that you ran it from the command line as has a correctly configured set of environment variables, in the case of \fIDBD::Oracle\fR, variables like \&\f(CW\*(C`ORACLE_HOME\*(C'\fR, \f(CW\*(C`ORACLE_SID\*(C'\fR or \f(CW\*(C`TWO_TASK\*(C'\fR. .PP The \f(CW\*(C`httpd\*(C'\fR process usually runs under the user id of \f(CW\*(C`nobody\*(C'\fR, which implies there is no configured environment. Any scripts attempting to execute in this situation will correctly fail. .PP One way to solve this problem is to set the environment for your database in a \&\f(CW\*(C`BEGIN { }\*(C'\fR block at the top of your script. Another technique is to configure your \s-1WWW\s0 server to pass-through certain environment variables to your \s-1CGI\s0 scripts. .PP Similarly, you should check your \f(CW\*(C`httpd\*(C'\fR error logfile for any clues, as well as the ``Idiot's Guide To Solving Perl / \s-1CGI\s0 Problems'' and ``Perl \s-1CGI\s0 Programming \s-1FAQ\s0'' for further information. It is unlikely the problem is DBI-related. .PP The ``Idiot's Guide To Solving Perl / \s-1CGI\s0 Problems'' can be located at: .PP .Vb 1 \& http://www.perl.com/perl/faq/index.html .Ve .PP as can the ``Perl \s-1CGI\s0 Programming \s-1FAQ\s0''. Read \fI\s-1BOTH\s0\fR these documents carefully! .ie n .SS "4.5 How do I get the number of rows returned from a ""SELECT"" statement?" .el .SS "4.5 How do I get the number of rows returned from a \f(CWSELECT\fP statement?" .IX Subsection "4.5 How do I get the number of rows returned from a SELECT statement?" Count them. Read the \s-1DBI\s0 docs for the \f(CW\*(C`rows()\*(C'\fR method. .SH "Miscellaneous Questions" .IX Header "Miscellaneous Questions" .SS "5.1 Can I do multi-threading with \s-1DBI\s0?" .IX Subsection "5.1 Can I do multi-threading with DBI?" Perl version 5.005 and later can be built to support multi-threading. The \s-1DBI\s0, as of version 1.02, does not yet support multi-threading so it would be unsafe to let more than one thread enter the \s-1DBI\s0 at the same time. .PP It is expected that some future version of the \s-1DBI\s0 will at least be thread-safe (but not thread-hot) by automatically blocking threads entering the \s-1DBI\s0 while it's already in use. .SS "5.2 How do I handle \s-1BLOB\s0 data with \s-1DBI\s0?" .IX Subsection "5.2 How do I handle BLOB data with DBI?" Handling \s-1BLOB\s0 data with the \s-1DBI\s0 is very straight-forward. \s-1BLOB\s0 columns are specified in a \s-1SELECT\s0 statement as per normal columns. However, you also need to specify a maximum \s-1BLOB\s0 size that the <I>database handle</I> can fetch using the \f(CW\*(C`LongReadLen\*(C'\fR attribute. .PP For example: .PP .Vb 3 \& ### $dbh is a connected database handle \& $sth = $dbh\->prepare( "SELECT blob_column FROM blobby_table" ); \& $sth\->execute; .Ve .PP would fail. .PP .Vb 3 \& ### $dbh is a connected database handle \& ### Set the maximum BLOB size... \& $dbh\->{LongReadLen} = 16384; ### 16Kb...Not much of a BLOB! \& \& $sth = $dbh\->prepare( "..." ); .Ve .PP would succeed <I>provided no column values were larger than the specified value</I>. .PP If the \s-1BLOB\s0 data is longer than the value of \f(CW\*(C`LongReadLen\*(C'\fR, then an error will occur. However, the \s-1DBI\s0 provides an additional piece of functionality that will automatically truncate the fetched \s-1BLOB\s0 to the size of \f(CW\*(C`LongReadLen\*(C'\fR if it is longer. This does not cause an error to occur, but may make your fetched \s-1BLOB\s0 data useless. .PP This behaviour is regulated by the \f(CW\*(C`LongTruncOk\*(C'\fR attribute which is set to a false value by default ( thus making overlong \s-1BLOB\s0 fetches fail ). .PP .Vb 3 \& ### Set BLOB handling such that it\*(Aqs 16Kb and can be truncated \& $dbh\->{LongReadLen} = 16384; \& $dbh\->{LongTruncOk} = 1; .Ve .PP Truncation of \s-1BLOB\s0 data may not be a big deal in cases where the \s-1BLOB\s0 contains run-length encoded data, but data containing checksums at the end, for example, a \s-1ZIP\s0 file, would be rendered useless. .SS "5.3 How can I invoke stored procedures with \s-1DBI\s0?" .IX Subsection "5.3 How can I invoke stored procedures with DBI?" The \s-1DBI\s0 does not define a database-independent way of calling stored procedures. .PP However, most database that support them also provide a way to call them from \s-1SQL\s0 statements \- and the \s-1DBI\s0 certainly supports that. .PP So, assuming that you have created a stored procedure within the target database, \fIeg\fR, an Oracle database, you can use \f(CW$dbh\fR\->\f(CW\*(C`do()\*(C'\fR to immediately execute the procedure. For example, .PP .Vb 1 \& $dbh\->do( "BEGIN someProcedure; END;" ); # Oracle\-specific .Ve .PP You should also be able to \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`execute\*(C'\fR, which is the recommended way if you'll be calling the procedure often. .SS "5.4 How can I get return values from stored procedures with \s-1DBI\s0?" .IX Subsection "5.4 How can I get return values from stored procedures with DBI?" .Vb 1 \& Contributed by Jeff Urlwin \& \& $sth = $dbh\->prepare( "BEGIN foo(:1, :2, :3); END;" ); \& $sth\->bind_param(1, $a); \& $sth\->bind_param_inout(2, \e$path, 2000); \& $sth\->bind_param_inout(3, \e$success, 2000); \& $sth\->execute; .Ve .PP Remember to perform error checking, though! ( Or use the \f(CW\*(C`RaiseError\*(C'\fR attribute ). .SS "5.5 How can I create or drop a database with \s-1DBI\s0?" .IX Subsection "5.5 How can I create or drop a database with DBI?" Database creation and deletion are concepts that are entirely too abstract to be adequately supported by \s-1DBI\s0. For example, Oracle does not support the concept of dropping a database at all! Also, in Oracle, the database \&\fIserver\fR essentially \fIis\fR the database, whereas in mSQL, the server process runs happily without any databases created in it. The problem is too disparate to attack in a worthwhile way. .PP Some drivers, therefore, support database creation and deletion through the private \f(CW\*(C`func()\*(C'\fR methods. You should check the documentation for the drivers you are using to see if they support this mechanism. .ie n .SS "5.6 How can I ""commit"" or ""rollback"" a statement with \s-1DBI\s0?" .el .SS "5.6 How can I \f(CWcommit\fP or \f(CWrollback\fP a statement with \s-1DBI\s0?" .IX Subsection "5.6 How can I commit or rollback a statement with DBI?" See the \f(CW\*(C`commit()\*(C'\fR and \f(CW\*(C`rollback()\*(C'\fR methods in the \s-1DBI\s0 Specification. .PP Chapter 6 of \*(L"Programming the Perl \s-1DBI\s0\*(R" discusses transaction handling within the context of \s-1DBI\s0 in more detail. .ie n .SS "5.7 How are ""NULL"" values handled by \s-1DBI\s0?" .el .SS "5.7 How are \f(CWNULL\fP values handled by \s-1DBI\s0?" .IX Subsection "5.7 How are NULL values handled by DBI?" \&\f(CW\*(C`NULL\*(C'\fR values in \s-1DBI\s0 are specified to be treated as the value \f(CW\*(C`undef\*(C'\fR. \&\f(CW\*(C`NULL\*(C'\fRs can be inserted into databases as \f(CW\*(C`NULL\*(C'\fR, for example: .PP .Vb 1 \& $rv = $dbh\->do( "INSERT INTO table VALUES( NULL )" ); .Ve .PP but when queried back, the \f(CW\*(C`NULL\*(C'\fRs should be tested against \f(CW\*(C`undef\*(C'\fR. This is standard across all drivers. .ie n .SS "5.8 What are these ""func()"" methods all about?" .el .SS "5.8 What are these \f(CWfunc()\fP methods all about?" .IX Subsection "5.8 What are these func() methods all about?" The \f(CW\*(C`func()\*(C'\fR method is defined within \s-1DBI\s0 as being an entry point for database-specific functionality, \fIeg\fR, the ability to create or drop databases. Invoking these driver-specific methods is simple, for example, to invoke a \f(CW\*(C`createDatabase\*(C'\fR method that has one argument, we would write: .PP .Vb 1 \& $rv =$dbh\->func( \*(Aqargument\*(Aq, \*(AqcreateDatabase\*(Aq ); .Ve .PP Software developers should note that the \f(CW\*(C`func()\*(C'\fR methods are non-portable between databases. .SS "5.9 Is \s-1DBI\s0 Year 2000 Compliant?" .IX Subsection "5.9 Is DBI Year 2000 Compliant?" \&\s-1DBI\s0 has no knowledge of understanding of what dates are. Therefore, \s-1DBI\s0 itself does not have a Year 2000 problem. Individual drivers may use date handling code internally and therefore be potentially susceptible to the Year 2000 problem, but this is unlikely. .PP You may also wish to read the ``Does Perl have a Year 2000 problem?'' section of the Perl \s-1FAQ\s0 at: .PP .Vb 1 \& http://www.perl.com/CPAN/doc/FAQs/FAQ/PerlFAQ.html .Ve .SH "Support and Training" .IX Header "Support and Training" The Perl5 Database Interface is \fI\s-1FREE\s0\fR software. \s-1IT\s0 \s-1COMES\s0 \s-1WITHOUT\s0 \s-1WARRANTY\s0 \&\s-1OF\s0 \s-1ANY\s0 \s-1KIND\s0. See the \s-1DBI\s0 \s-1README\s0 for more details. .PP However, some organizations are providing either technical support or training programs on \s-1DBI\s0. The present author has no knowledge as to the quality of these services. The links are included for reference purposes only and should not be regarded as recommendations in any way. \&\fICaveat emptor\fR. .SS "Commercial Support" .IX Subsection "Commercial Support" .IP "The Perl Clinic" 4 .IX Item "The Perl Clinic" The Perl Clinic provides commercial support for \fIPerl\fR and Perl related problems, including the \fI\s-1DBI\s0\fR and its drivers. Support is provided by the company with whom Tim Bunce, author of \fI\s-1DBI\s0\fR and \&\fIDBD::Oracle\fR, works and ActiveState. For more information on their services, please see: .Sp .Vb 1 \& http://www.perlclinic.com .Ve .SS "Training" .IX Subsection "Training" .IP "Westlake Solutions" 4 .IX Item "Westlake Solutions" A hands-on class for experienced Perl \s-1CGI\s0 developers that teaches how to write database-connected \s-1CGI\s0 scripts using Perl and \s-1DBI\s0.pm. This course, along with four other courses on \s-1CGI\s0 scripting with Perl, is taught in Washington, \s-1DC\s0; Arlington, Virginia; and on-site worldwide upon request. .Sp See: .Sp .Vb 1 \& http://www.westlake.com/training .Ve .Sp for more details. .SH "Other References" .IX Header "Other References" In this section, we present some miscellaneous \s-1WWW\s0 links that may be of some interest to \s-1DBI\s0 users. These are not verified and may result in unknown sites or missing documents. .PP .Vb 3 \& http://www\-ccs.cs.umass.edu/db.html \& http://www.odmg.org/odmg93/updates_dbarry.html \& http://www.jcc.com/sql_stnd.html .Ve .SH "AUTHOR" .IX Header "AUTHOR" Alligator Descartes. Portions are Copyright their original stated authors. .SH "COPYRIGHT" .IX Header "COPYRIGHT" This document is Copyright (c)1994\-2000 Alligator Descartes, with portions Copyright (c)1994\-2000 their original authors. This module is released under the 'Artistic' license which you can find in the perl distribution. .PP This document is Copyright (c)1997\-2000 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 credits and copyright notices are retained ( the \fI\s-1AUTHOR\s0\fR and \fI\s-1COPYRIGHT\s0\fR sections ). Requests for other distribution rights, including incorporation into commercial products, such as books, magazine articles or CD-ROMs should be made to Alligator Descartes.
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