Manual Pages for UNIX Darwin command on man DBI::FAQ

DBI::FAQ(3) User Contributed Perl Documentation DBI::FAQ(3)

NAME

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

Interface

SYNOPSIS

perldoc DBI::FAQ

VVEERRSSIIOONN This document is currently at version 0.38, as of February 8th, 2000.

DESCRIPTION

This document serves to answer the most frequently asked questions on both the DBI Mailing Lists and personally to members of the DBI development team. BBaassiicc IInnffoorrmmaattiioonn && IInnffoorrmmaattiioonn SSoouurrcceess 11..11 WWhhaatt iiss DDBBII,, DDBBppeerrll,, OOrraappeerrll aanndd **ppeerrll?? 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 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 API defined by DBI will work on all these database types. A similar benefit is gained by the ability to connect to two different databases of different vendor within the one perl script, ie, I want to read data from an Oracle database and insert it back into an Informix database all within one program. The DBI layer allows you to do this simply and powerfully. DBperl is the old name for the interface specification. It's usually now used to denote perl4 modules on database interfacing, such as, oraperl, isqlperl, ingperl and so on. These interfaces didn't have a standard API and are generally not supported. Here's a list of DBperl modules, their corresponding DBI counterparts and support information. Please note, the author's listed here generally do not maintain the DBI module for the same database. These email addresses are unverified and should only be used for queries concerning the perl4 modules listed below. DBI driver queries should be

directed to the dbi-users mailing list.

Module Name Database Required Author DBI

------ --------- --- --

Sybperl Sybase Michael Peppler DBD::Sybase Oraperl Oracle 6 & 7 Kevin Stock DBD::Oracle

Ingperl Ingres Tim Bunce & DBD::Ingres Ted Lemon

Interperl Interbase Buzz Moschetti DBD::Interbase Uniperl Unify 5.0 Rick Wargo None Pgperl Postgres Igor Metz DBD::Pg Btreeperl NDBM John Conover SDBM?

Ctreeperl C-Tree John Conover None

Cisamperl Informix C-ISAM Mathias Koerber None

Duaperl X.500 Directory Eric Douglas None User Agent However, some DBI modules have DBperl emulation layers, so, DBD::Oracle comes with an Oraperl emulation layer, which allows you to run legacy oraperl scripts without modification. The emulation layer translates the oraperl API calls into DBI calls and executes them through the DBI switch. Here's a table of emulation layer information: 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

The Msqlperl emulation is a special case. Msqlperl is a perl5 driver for mSQL databases, but does not conform to the DBI Specification. It's use is being deprecated in favour of DBD::mSQL. Msqlperl may be downloaded from CPAN via:

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

11..22.. WWhheerree ccaann II ggeett iitt ffrroomm?? The Comprehensive Perl Archive Network resources should be used for

retrieving up-to-date versions of the DBI and drivers. CPAN may be

accessed via Tom Christiansen's splendid CPAN multiplexer program located at: http://www.perl.com/CPAN/ For more specific version information and exact URLs of drivers, please see the DBI drivers list and the DBI module pages which can be found on: http://dbi.perl.org/ http://www.symbolstone.org/technology/perl/DBI This list is automatically generated on a nightly basis from CPAN and

should be up-to-date.

11..33.. WWhheerree ccaann II ggeett mmoorree iinnffoorrmmaattiioonn?? There are a few information sources on DBI. "Programming the Perl DBI" "Programming the Perl DBI" is the official book on the DBI written by Alligator Descartes and Tim Bunce and published by O'Reilly & Associates. The book was released on February 9th, 2000. The table of contents is: 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 The book should be available from all good bookshops and can be ordered online either via O'Reilly & Associates http://www.oreilly.com/catalog/perldbi or Amazon http://www.amazon.com/exec/obidos/ASIN/1565926994/dbi POD documentation PODs are chunks of documentation usually embedded within perl programs that document the code ``in place'', providing a useful resource for programmers and users of modules. POD for DBI and drivers is beginning to become more commonplace, and documentation for these modules can be read with the "perldoc" program included with Perl. The DBI Specification The POD for the DBI Specification can be read with the: perldoc DBI command. The Specification also forms Appendix A of "Programming the Perl DBI". Oraperl Users of the Oraperl emulation layer bundled with DBD::Oracle, may read up 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 by Kevin Stock for perl4. The oraperl API is fully listed and described there. Drivers Users of the DBD modules may read about some of the private functions and quirks of that driver by typing: perldoc

For example, the DBD::mSQL driver is bundled with driver-

specific documentation that can be accessed by typing perldoc DBD::mSQL Frequently Asked Questions This document, the Frequently Asked Questions is also available as POD documentation! 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. The DBI::FAQ module

should be downloaded and installed for the more up-to-date

version.

The version of DBI::FAQ shipped with the "DBI" module may be

slightly out of date. POD in general Information on writing POD, and on the philosophy of POD in general, can be read by typing: perldoc perlpod Users with the Tk module installed may be interested to learn

there is a Tk-based POD reader available called "tkpod", which

formats POD in a convenient and readable way. This is available via CPAN as the module called Tk::POD and is highly recommended. Driver and Database Characteristics The driver summaries that were produced for Appendix B of "Programming the Perl DBI" are available online at: http://dbi.perl.org/ http://www.symbolstone.org/technology/perl/DBI 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 DBI Specification. Rambles, Tidbits and Observations http://dbi.perl.org/tidbits http://www.symbolstone.org/technology/perl/DBI/tidbits There are a series of occasional rambles from various people on the DBI 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. Articles A list of articles discussing the DBI can be found on the DBI WWW page at: http://dbi.perl.org/ http://www.symbolstone.org/technology/perl/DBI 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. README files The README 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 DBI WWW page at: http://dbi.perl.org/ http://www.symbolstone.org/technology/perl/DBI Mailing Lists There are three mailing lists for DBI:

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)

For information on how to subscribe, set digest mode etc, and unsubscribe, send an email message (the content will be ignored) to:

dbi-announce-help@perl.org

dbi-users-help@perl.org

dbi-dev-help@perl.org

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 the much 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. CCoommppiillaattiioonn PPrroobblleemmss 22..11.. CCoommppiillaattiioonn pprroobblleemmss oorr ""IItt ffaaiillss tthhee tteesstt!!"" First off, consult the README 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 README files for each driver in advance online at: http://dbi.perl.org/ http://www.symbolstone.org/technology/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: +o What the problem was, and test cases, if possible. +o What you needed to do to fix it. Please make sure you mention everything. +o Platform information, database version, perl version, module version and DBI version. Email the author Do NOT whinge! Please email the address listed in the WWW pages for whichever driver you are having problems with. Do not directly email the author at a known address unless it corresponds with the one listed. We tend to have real jobs to do, and we do read the mailing lists for problems. Besides, we may not have access to favourite brain-damaged platform here> and couldn't be of any

assistance 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're doing this sort of stuff anyway, and get a patch within 5 minutes. The atmosphere 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 information as possible, ie: +o ALL the information asked for in the README file in the problematic module. And we mean ALL of it. We don't put lines like that in documentation for the good of our health, or to meet obscure README file standards of length. +o If you have a core dump, try the Devel::CoreStack module for generating 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/cpanmod?module=Devel::CoreStack

+o Module versions, perl version, test cases, operating system versions and 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. Finally, please be aware that some authors, including Tim Bunce, specifically request that you do not mail them directly. Please respect their wishes and use the email addresses listed in the appropriate module "README" file.

Email the dbi-users Mailing List

It's usually a fairly intelligent idea to cc the mailing list anyway with problems. The authors all read the lists, so you lose nothing by mailing there. PPllaattffoorrmm aanndd DDrriivveerr IIssssuueess 33..11 WWhhaatt''ss tthhee ddiiffffeerreennccee bbeettwweeeenn OODDBBCC aanndd DDBBII??

In terms of architecture - not much: Both define programming

interfaces. Both allow multiple drivers to be loaded to do the actual work.

In terms of ease of use - much: The DBI is a 'high level' interface

that, like Perl itself, strives to make the simple things easy while still making the hard things possible. The ODBC is a 'low level'

interface. All nuts-bolts-knobs-and-dials.

Now there's an ODBC driver for the DBI (DBD::ODBC) the "What's the difference" question is more usefully rephrased as: Chapter 7 of "Programming the Perl DBI" covers this topic in far more detail and should be consulted. 33..22 WWhhaatt''ss tthhee ddiiffffeerreennccee bbeettwweeeenn WWiinn3322::::OODDBBCC aanndd DDBBDD::::OODDBBCC?? The DBI, and thus DBD::ODBC, has a different philosophy from the Win32::ODBC module:

The Win32::ODBC module is a 'thin' layer over the low-level ODBC API.

The DBI defines a simpler 'higher level' interface. The Win32::ODBC module gives you access to more of the ODBC API. The DBI and DBD::ODBC give you access to only the essentials. (But, unlike Win32::ODBC, the DBI and DBD::ODBC do support parameter binding and multiple prepared statements which reduces the load on the database server and can dramatically increase performance.) The Win32::ODBC module only works on Win32 systems. The DBI and DBD::ODBC are very portable and work on Win32 and Unix. The DBI and DBD::ODBC 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).

Scripts written with the DBI and DBD::ODBC are faster than Win32::ODBC on Win32 and are trivially portable to other supported database types. The DBI offers optional automatic printing or die()ing on errors which makes applications simpler and more robust. The current DBD::ODBC driver version 0.16 is new and not yet fully stable. A new release is due soon [relative to the date of the next

TPJ issue :-] and will be much improved and offer more ODBC

functionality. To summarise: The Win32::ODBC module is your best choice if you need access to more of the ODBC API than the DBI gives you. Otherwise, the DBI and DBD::ODBC combination may be your best bet. Chapter 7 of "Programming the Perl DBI" covers this topic in far more detail and should be consulted. 33..33 IIss DDBBII ssuuppppoorrtteedd uunnddeerr WWiinnddoowwss 9955 // NNTT ppllaattffoorrmmss?? Finally, yes! Jeff Urlwin has been working diligently on building DBI and DBD::ODBC under these platforms, and, with the advent of a stabler perl and a port of MakeMaker, the project has come on by great leaps and bounds. The DBI and DBD::Oracle Win32 ports are now a standard part of DBI, so, downloading DBI of version higher than 0.81 should work fine as should using the most recent DBD::Oracle version.

33..44 CCaann II aacccceessss MMiiccrroossoofftt AAcccceessss oorr SSQQLL-SSeerrvveerr ddaattaabbaasseess wwiitthh DDBBII??

Yes, use the DBD::ODBC driver. 33..55 IIss tthhee aa DDBBDD ffoorr <>?? Is is listed on the DBI drivers page? http://dbi.perl.org/ http://www.symbolstone.org/technology/perl/DBI If not, no. A complete absence of a given database driver from that

page means that no-one has announced any intention to work on it, not

that such a driver is impossible to write. A corollary of the above statement implies that if you see an announcement for a driver not on the above page, there's a good chance it's not actually a DBI driver, and may not conform to the specifications. Therefore, questions concerning problems with that code should not really be addressed to the DBI Mailing Lists. 33..66 WWhhaatt''ss DDBBMM?? AAnndd wwhhyy sshhoouulldd II uussee DDBBII iinnsstteeaadd??

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 AnyDBMFile module.'' To sum up, DBM is a perfectly satisfactory solution for essentially

read-only databases, or small and simple datasets. However, for more

scaleable dataset handling, not to mention robust transactional locking, users are recommended to use a more powerful database engine via DBI. Chapter 2 of "Programming the Perl DBI" discusses DBM files in detail. 33..77 WWhhaatt ddaattaabbaassee ddoo yyoouu rreeccoommmmeenndd mmee uussiinngg?? 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. 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 mSQL 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 WWW site at: http://www.hughes.com.au You may also wish to look at MySQL which is a more powerful database engine that has a similar feel to mSQL. http://www.tcx.se 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 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 are

several differences between Oracle and Informix which are too complex for this document to detail. Information on Informix can be found on their WWW site at: http://www.informix.com In the case of WWW fronted applications, mSQL may be a better option due to slow connection times between a CGI script and the Oracle RDBMS and also the amount of resource each Oracle connection will consume.

mSQL is 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 provided as-is.

33..88 IIss <> ssuuppppoorrtteedd iinn DDBBII?? 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 no. DBI reflects a generic API that will work for most databases, and has

no database-specific functionality.

However, driver authors may, if they so desire, include hooks to

database-specific functionality through the "func()" method defined in

the DBI API. Script developers should note that use of functionality provided via the "func()" methods is very unlikely to be portable across databases. PPrrooggrraammmmiinngg QQuueessttiioonnss 44..11 IIss DDBBII aannyy uussee ffoorr CCGGII pprrooggrraammmmiinngg?? In a word, yes! DBI is hugely useful for CGI programming! In fact, I would tentatively say that CGI programming is one of two top uses for DBI.

DBI confers the ability to CGI programmers to power WWW-fronted

databases to their users, which provides users with vast quantities of ordered data to play with. DBI 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 CGI scripts. 44..22 HHooww ddoo II ggeett ffaasstteerr ccoonnnneeccttiioonn ttiimmeess wwiitthh DDBBDD::::OOrraaccllee aanndd CCGGII?? Contributed by John D. Groenveld The Apache "httpd" maintains a pool of "httpd" children to service client requests. Using the Apache modperl 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 modperl module can be downloaded from CPAN via:

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

44..33 HHooww ddoo II ggeett ppeerrssiisstteenntt ccoonnnneeccttiioonnss wwiitthh DDBBII aanndd CCGGII?? 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/cpanmod?module=Apache::DBI

44..44 ````WWhheenn II rruunn aa ppeerrll ssccrriipptt ffrroomm tthhee ccoommmmaanndd lliinnee,, iitt wwoorrkkss,, bbuutt,, wwhheenn II rruunn iitt uunnddeerr tthhee ""hhttttppdd"",, iitt ffaaiillss!!'''' WWhhyy?? 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 DBD::Oracle, variables like "ORACLEHOME", "ORACLESID" or "TWOTASK". The "httpd" process usually runs under the user id of "nobody", which implies there is no configured environment. Any scripts attempting to execute in this situation will correctly fail. One way to solve this problem is to set the environment for your database in a "BEGIN { }" block at the top of your script. Another

technique is to configure your WWW server to pass-through certain

environment variables to your CGI scripts. Similarly, you should check your "httpd" error logfile for any clues, as well as the ``Idiot's Guide To Solving Perl / CGI Problems'' and ``Perl CGI Programming FAQ'' for further information. It is unlikely

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! 44..55 HHooww ddoo II ggeett tthhee nnuummbbeerr ooff rroowwss rreettuurrnneedd ffrroomm aa ""SSEELLEECCTT"" ssttaatteemmeenntt?? Count them. Read the DBI docs for the "rows()" method. MMiisscceellllaanneeoouuss QQuueessttiioonnss

55..11 CCaann II ddoo mmuullttii-tthhrreeaaddiinngg wwiitthh DDBBII??

Perl version 5.005 and later can be built to support multi-threading.

The DBI, as of version 1.02, does not yet support multi-threading so it

would be unsafe to let more than one thread enter the DBI at the same time. It is expected that some future version of the DBI will at least be

thread-safe (but not thread-hot) by automatically blocking threads

intering the DBI while it's already in use.

For some OCI example code for Oracle that has multi-threaded "SELECT"

statements, see: http://www.symbolstone.org/technology/oracle/oci/orathreads.tar.gz 55..22 HHooww ddoo II hhaannddllee BBLLOOBB ddaattaa wwiitthh DDBBII??

Handling BLOB data with the DBI is very straight-forward. BLOB columns

are specified in a SELECT statement as per normal columns. However, you also need to specify a maximum BLOB size that the database handle can fetch using the "LongReadLen" attribute. For example:

### $dbh is a connected database handle

$sth = $dbh->prepare( "SELECT blobcolumn FROM blobbytable" );

$sth->execute;

would fail.

### $dbh is a connected database handle

### Set the maximum BLOB size...

$dbh->{LongReadLen} = 16384; ### 16Kb...Not much of a BLOB!

$sth = $dbh->prepare( "..." );

would succeed provided no column values were larger than the specified value. If the BLOB data is longer than the value of "LongReadLen", then an error will occur. However, the DBI provides an additional piece of functionality that will automatically truncate the fetched BLOB to the size of "LongReadLen" if it is longer. This does not cause an error to occur, but may make your fetched BLOB data useless. This behaviour is regulated by the "LongTruncOk" attribute which is defaultly set to a false value ( thus making overlong BLOB fetches fail ).

### Set BLOB handling such that it's 16Kb and can be truncated

$dbh->{LongReadLen} = 16384;

$dbh->{LongTruncOk} = 1;

Truncation of BLOB data may not be a big deal in cases where the BLOB

contains run-length encoded data, but data containing checksums at the

end, for example, a ZIP file, would be rendered useless. 55..33 HHooww ccaann II iinnvvookkee ssttoorreedd pprroocceedduurreess wwiitthh DDBBII??

The DBI does not define a database-independent way of calling stored

procedures. However, most database that support them also provide a way to call

them from SQL statements - and the DBI certainly supports that.

So, assuming that you have created a stored procedure within the target

database, eg, an Oracle database, you can use $dbh->"do()" to

immediately execute the procedure. For example,

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

You should also be able to "prepare" and "execute", which is the recommended way if you'll be calling the procedure often. 55..44 HHooww ccaann II ggeett rreettuurrnn vvaalluueess ffrroomm ssttoorreedd pprroocceedduurreess wwiitthh DDBBII?? Contributed by Jeff Urlwin

$sth = $dbh->prepare( "BEGIN foo(:1, :2, :3); END;" );

$sth->bindparam(1, $a);

$sth->bindparaminout(2, \$path, 2000);

$sth->bindparaminout(3, \$success, 2000);

$sth->execute;

Remember to perform error checking, though! ( Or use the "RaiseError" attribute ). 55..55 HHooww ccaann II ccrreeaattee oorr ddrroopp aa ddaattaabbaassee wwiitthh DDBBII?? Database creation and deletion are concepts that are entirely too abstract to be adequately supported by DBI. For example, Oracle does not support the concept of dropping a database at all! Also, in Oracle, the database server essentially is 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. Some drivers, therefore, support database creation and deletion through the private "func()" methods. You should check the documentation for the drivers you are using to see if they support this mechanism. 55..66 HHooww ccaann II ""ccoommmmiitt"" or "rollback" a statement with DBI? See the "commit()" and "rollback()" methods in the DBI Specification. Chapter 6 of "Programming the Perl DBI" discusses transaction handling within the context of DBI in more detail. 55..77 HHooww aarree ""NNUULLLL"" vvaalluueess hhaannddlleedd bbyy DDBBII?? "NULL" values in DBI are specified to be treated as the value "undef". "NULL"s can be inserted into databases as "NULL", for example:

$rv = $dbh->do( "INSERT INTO table VALUES( NULL )" );

but when queried back, the "NULL"s should be tested against "undef". This is standard across all drivers. 55..88 WWhhaatt aarree tthheessee ""ffuunncc(())"" mmeetthhooddss aallll aabboouutt?? The "func()" method is defined within DBI as being an entry point for

database-specific functionality, eg, the ability to create or drop

databases. Invoking these driver-specific methods is simple, for

example, to invoke a "createDatabase" method that has one argument, we would write:

$rv =$dbh->func( 'argument', 'createDatabase' );

Software developers should note that the "func()" methods are non-

portable between databases. 55..99 IIss DDBBII YYeeaarr 22000000 CCoommpplliiaanntt?? DBI has no knowledge of understanding of what dates are. Therefore, DBI 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. You may also wish to read the ``Does Perl have a Year 2000 problem?'' section of the Perl FAQ at: http://www.perl.com/CPAN/doc/FAQs/FAQ/PerlFAQ.html SSuuppppoorrtt aanndd TTrraaiinniinngg The Perl5 Database Interface is FREE software. IT COMES WITHOUT WARRANTY OF ANY KIND. See the DBI README for more details. However, some organizations are providing either technical support or training programs on DBI. 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. Caveat emptor. CCoommmmeerrcciiaall SSuuppppoorrtt The Perl Clinic The Perl Clinic provides commercial support for Perl and Perl related problems, including the DBI and its drivers. Support is provided by the company with whom Tim Bunce, author of DBI and DBD::Oracle, works and ActiveState. For more information on their services, please see: http://www.perlclinic.com TTrraaiinniinngg Westlake Solutions

A hands-on class for experienced Perl CGI developers that teaches

how to write database-connected CGI scripts using Perl and DBI.pm.

This course, along with four other courses on CGI scripting with

Perl, is taught in Washington, DC; Arlington, Virginia; and on-site

worldwide upon request. See: http://www.westlake.com/training for more details. OOtthheerr RReeffeerreenncceess In this section, we present some miscellaneous WWW links that may be of some interest to DBI users. These are not verified and may result in unknown sites or missing documents.

http://www-ccs.cs.umass.edu/db.html

http://www.odmg.org/odmg93/updatesdbarry.html http://www.jcc.com/sqlstnd.html AUTHOR Alligator Descartes . Portions are Copyright their original stated authors. COPYRIGHT

released under the 'Artistic' license which you can find in the perl distribution.

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 AUTHOR and COPYRIGHT 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 .