DBI::FAQ(3) User Contributed Perl Documentation DBI::FAQ(3)NAMEDBI::FAQ-- The Frequently Asked Questions for the Perl5 Database
Interface
SYNOPSIS
perldoc DBI::FAQVERSION
This document is currently at version 0.38, as of February 8th, 2000.
That's very old. A newer FAQ can be found at
<http://faq.dbi-support.com/>
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.
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
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
<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
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/cpan_mod?module=Msqlperl
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 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.
1.3. Where can I get more information?
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 <I>via</I> 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 <driver>
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.
Compilation Problems
2.1. Compilation problems or "It fails the test!"
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:
· 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, 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 <insert your
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:
· 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.
· 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/cpan_mod?module=Devel::CoreStack
· 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.
Platform and Driver Issues
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.
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.
3.2 What's the difference between Win32::ODBC and DBD::ODBC?
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.
3.3 Is DBI supported under Windows 95 / NT platforms?
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.
3.4 Can I access Microsoft Access or SQL-Server databases with DBI?
Yes, use the DBD::ODBC driver.
3.5 Is the a DBD for <insert favourite database here>?
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.
3.6 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-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.
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.
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.
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 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.
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
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.
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 ``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 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 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!
4.5 How do I get the number of rows returned from a "SELECT" statement?
Count them. Read the DBI docs for the "rows()" method.
Miscellaneous Questions
5.1 Can I do multi-threading with DBI?
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
5.2 How do I handle BLOB data with DBI?
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 <I>database
handle</I> can fetch using the "LongReadLen" attribute.
For example:
### $dbh is a connected database handle
$sth = $dbh->prepare( "SELECT blob_column FROM blobby_table" );
$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 <I>provided no column values were larger than the
specified value</I>.
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.
5.3 How can I invoke stored procedures with DBI?
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.
5.4 How can I get return values from stored procedures with DBI?
Contributed by Jeff Urlwin
$sth = $dbh->prepare( "BEGIN foo(:1, :2, :3); END;" );
$sth->bind_param(1, $a);
$sth->bind_param_inout(2, \$path, 2000);
$sth->bind_param_inout(3, \$success, 2000);
$sth->execute;
Remember to perform error checking, though! ( Or use the "RaiseError"
attribute ).
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 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.
5.6 How can I "commit" 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.
5.7 How are "NULL" values handled by DBI?
"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.
5.8 What are these "func()" methods all about?
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.
5.9 Is DBI Year 2000 Compliant?
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
Support and Training
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.
Commercial Support
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
Training
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.
Other References
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/updates_dbarry.html
http://www.jcc.com/sql_stnd.html
AUTHOR
Alligator Descartes <http://www.symbolstone.org/descarte/contact.html>.
Portions are Copyright their original stated authors.
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.
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 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 <http://www.symbolstone.org/descarte/contact.html>.
perl v5.10.0 2007-11-15 DBI::FAQ(3)
