Appendix D: Perl DBI

Overview

The recommended way to connect to a database (not only to MySQL) in Perl is with the DBI module. This is a generic interface that allows you to access different kinds of databases in the same way. Along with the DBI module, you need a DBD module. Each DBD module is for a specific database; you should use the one associated with MySQL.

Throughout this appendix, you'll see the following conventions for variable names:

$dbh A database handle object, returned from the connect() or connect_cached() methods

$sth A statement handle object, returned from a prepare() method among others

$drh A driver handle object (rarely used in applications)

$h A database, statement, or driver handle

$rc A Boolean return code (true for success or false for an error)

$rv A return value of sorts, usually an integer

@ary An array of values, usually a row of data returned from a query

$rowsThe number of rows processed, or -1 if unknown

$fh A file handle

undef A NULL, or undefined, value

\%attributes A reference to a hash of attribute values, used for various purposes by the methods

To use the DBI, you need to load the DBI module at the beginning of your script, as follows:

use DBI;

Then, you need to return a database handle, usually with the connect() DBI class method. The database handle then accesses methods that can run queries and return results, usually returning a statement handle.