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The archives are listed at the end of this document and on the DBI home page http: To help you make the best use of the dbi-users mailing list, and any other lists or forums you may use, I recommend that you read "Getting Answers" by Mike Ash: This is the best way to get help.
You don't have to subscribe to the list in order to post, though I'd recommend it. You can get help on subscribing and using the list by emailing dbi-users-help perl. Please note that Tim Bunce does not maintain the mailing lists or the web pages generous volunteers do that. So please don't send mail directly to him; he just doesn't have the time to answer questions personally. The dbi-users mailing list has lots of experienced people who should be able to help you if you need it.
If you do email Tim he is very likely to just forward it to the mailing list. StackOverflow has a DBI tag http: The DBI home page at http: They include links to other resources, but are rather out-dated. If you think you've found a memory leak then read "Memory Leaks".
Your problem is most likely related to the specific DBD driver module you're using. If that's the case then click on the 'Bugs' link on the http: Only submit a bug report against the DBI itself if you're sure that your issue isn't related to the driver you're using. The significant user-visible changes in each release are documented in the DBI:: Changes module so you can read them by executing perldoc DBI:: Some DBI changes require changes in the drivers, but the drivers can take some time to catch up.
Newer versions of the DBI have added features that may not yet be supported by the drivers you use. Talk to the authors of your drivers if you need a new feature that is not yet supported. Features added after DBI 1. See "Naming Conventions and Name Space". DBI extension modules can be found at https: And all modules related to the DBI can be found at https: The DBI is a database access module for the Perl programming language.
It defines a set of methods, variables, and conventions that provide a consistent database interface, independent of the actual database being used. It is important to remember that the DBI is just an interface. The DBI is a layer of "glue" between an application and one or more database driver modules.
It is the driver modules which do most of the real work. The DBI provides a standard interface and framework for the drivers to operate within. This document often uses terms like references , objects , methods.
If you're not familiar with those terms then it would be a good idea to read at least the following perl manuals first: The DBI "dispatches" the method calls to the appropriate driver for actual execution. The DBI is also responsible for the dynamic loading of drivers, error checking and handling, providing default implementations for methods, and many other non-database specific duties. Each driver contains implementations of the DBI methods using the private interface functions of the corresponding database engine.
Note that Perl will automatically destroy database and statement handle objects if all references to them are deleted. Then you need to "connect" to your data source and get a handle for that connection:.
Since connecting can be expensive, you generally just connect at the start of your program and disconnect at the end. Explicitly defining the required AutoCommit behaviour is strongly recommended and may become mandatory in a later version. This determines whether changes are automatically committed to the database when executed, or need to be explicitly committed later.
The DBI allows an application to "prepare" statements for later execution. A prepared statement is identified by a statement handle held in a Perl variable.
To commit your changes to the database when "AutoCommit" is off:. Finally, when you have finished working with the data source, you should "disconnect" from it:.
The DBI does not have a concept of a "current session". Every session has a handle object i. That handle object is used to invoke database related methods.
Most data is returned to the Perl script as strings. Null values are returned as undef. This allows arbitrary precision numeric data to be handled without loss of accuracy. Beware that Perl may not preserve the same accuracy when the string is used as a number.
Dates and times are returned as character strings in the current default format of the corresponding database engine. Perl supports binary data in Perl strings, and the DBI will pass binary data to and from the driver without change. It is up to the driver implementors to decide how they wish to handle such binary data. Perl supports two kinds of strings: Unicode utf8 internally and non-Unicode defaults to iso if forced to assume an encoding.
Drivers should accept both kinds of strings and, if required, convert them to the character set of the database being used. Similarly, when fetching from the database character data that isn't iso the driver should convert it into utf8.
Non-sequential record reads are not supported in this version of the DBI. In other words, records can only be fetched in the order that the database returned them, and once fetched they are forgotten.
Positioned updates and deletes are not directly supported by the DBI. See the description of the CursorName attribute for an alternative. Private driver functions can be invoked using the DBI func method. Private driver attributes are accessed just like standard attributes. Extensions and related modules use the DBIx:: Package names beginning with DBD:: The letter case used for attribute names is significant and plays an important part in the portability of DBI scripts.
The case of the attribute name is used to signify who defined the meaning of that name and its values. It is of the utmost importance that Driver developers only use lowercase attribute names when defining private attributes. Private attribute names must be prefixed with the driver name or suitable abbreviation e. The DBI itself does not mandate or require any particular language to be used; it is language independent.
The only requirement is that queries and other statements must be expressed as a single string of characters passed as the first argument to the "prepare" or "do" methods. Some drivers support placeholders and bind values. Placeholders , also called parameter markers, are used to indicate values in a database statement that will be supplied later, before the prepared statement is executed.
The association of actual values with placeholders is known as binding , and the values are referred to as bind values. Some drivers also allow placeholders like: Check your driver documentation.
The driver will remove the backslash character and ignore the placeholder, passing it unchanged to the backend. With most drivers, placeholders can't be used for any element of a statement that would prevent the database server from validating the statement and creating a query execution plan for it.
Also, placeholders can only represent single scalar values. For example, the following statement won't work as expected for more than one value:. So you should use " Undefined values, or undef , are used to indicate NULL values. These examples insert and update the column age with a NULL value:.
At least for database engines that conform to the SQL standard. A simple technique is to prepare the appropriate statement as needed, and substitute the placeholder for non-NULL cases:.
The techniques above call prepare for the SQL statement with each call to execute. Because calls to prepare can be expensive, performance can suffer when an application iterates many times over statements like the above. Its SQL statement would need to be prepared only once for all cases, thus improving performance.
But each example lacks portability, robustness, or simplicity. Whether an example is supported on your database engine depends on what SQL extensions it provides, and where it supports the? The arguments are required, whether their values are defined or undef.
Example 0 should not work as mentioned earlier , but may work on a few database engines anyway e. Example 0 is part of examples 4, 5, and 6, so if example 0 works, these other examples may work, even if the engine does not properly support the right hand side of the OR expression. Examples 1 and 2 are not robust: That means you must have some notion of what data won't be stored in the column, and expect clients to adhere to that.
Example 6, the least simple, is probably the most portable, i. Here is a table that indicates which examples above are known to work on various database engines:.