ZEND PHP 5 Certification STUDY GUIDE

156 ” Database Programming
PHP Data Objects (PDO)
The standard distribution of PHP 5.1 and greater includes PDO and the drivers for
SQLite by default. However, there are many other database drivers for PDO, including
Microsoft SQL Server, Firebird, MySQL, Oracle, PostgreSQL, and ODBC. Refer to
the PDO documentation on the PHP Web site for details on how to install each of
these drivers. Once installed, the process for using each driver is, for the most part,
the same because PDO provides a unified data access layer to each of these database
engines. There is no longer a need for separate mysql_query() or pg_query() functions.
PDO provides a single object-oriented interface to these databases.
The difference comes in the SQL used for each database since each database engine
provides its own specialized keywords. PDO does not provide a means for standardizing
statements across database engines. Thus, when switching an application
from one database to another, you will need to pay careful attention to the SQL statements
issued from your application to ensure that they do not contain keywords and
functionality that the new database engine does not recognize.
Connecting To a Database With PDO
To connect to a database, PDO requires at least a Data Source Name, or DSN, formatted
according to the driver used. Detailed DSN formatting documentation exists on
the PHP Web site for each driver. Additionally, if your database requires a username
or password, PDO will need these to access the database. A sample connection to a
MySQL database using the library database described earlier might look like this:
$dsn = ’mysql:host=localhost;dbname=library’;
$dbh = new PDO($dsn, ’dbuser’, ’dbpass’);
Since each of these examples assumes a MySQL database, it’s worth mentioning here
that the MySQL client library contains a few quirks that cause some irregularities
when using the PDO_MYSQL driver, specifically with regard to prepared statements.
To solve these irregularities it is necessary to set a PDO attribute after connecting
to the database. The following line of code will set PDO to use its own native query
parser for prepared statements instead of the MySQL client library API.
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