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410 lines
12 KiB
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<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<chapter xml:id="mysqli.overview" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Overview</title>
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<para>
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This section provides an introduction to the options available to
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you when developing a PHP application that needs to interact with a
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MySQL database.
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</para>
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<para>
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<emphasis role="bold">What is an API?</emphasis>
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</para>
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<para>
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An Application Programming Interface, or API, defines the classes,
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methods, functions and variables that your application will need to
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call in order to carry out its desired task. In the case of PHP
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applications that need to communicate with databases the necessary
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APIs are usually exposed via PHP extensions.
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</para>
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<para>
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APIs can be procedural or object-oriented. With a procedural API, you
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call functions to carry out tasks, with the object-oriented API you
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instantiate classes and then call methods on the resulting objects.
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Of the two, the latter is usually the preferred interface, as it is
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more modern and leads to better-organized code.
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</para>
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<para>
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When writing PHP applications that need to connect to the MySQL
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server there are several API options available. This document
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discusses what is available and how to select the best solution for
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your application.
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</para>
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<para>
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<emphasis role="bold">What is a Connector?</emphasis>
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</para>
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<para>
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In the MySQL documentation, the term <emphasis>connector</emphasis>
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refers to a piece of software that allows your application to
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connect to the MySQL database server. MySQL provides connectors for
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a variety of languages, including PHP.
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</para>
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<para>
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If your PHP application needs to communicate with a database server
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you will need to write PHP code to perform such activities as
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connecting to the database server, querying the database, and other
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database-related functions. Software is required to provide the API
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that your PHP application will use, and also handle the
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communication between your application and the database server,
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possibly using other intermediate libraries where necessary. This
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software is known generically as a connector, as it allows your
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application to <emphasis>connect</emphasis> to a database server.
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</para>
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<para>
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<emphasis role="bold">What is a Driver?</emphasis>
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</para>
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<para>
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A driver is a piece of software designed to communicate with a
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specific type of database server. The driver may also call a
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library, such as the MySQL Client Library or the MySQL Native
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Driver. These libraries implement the low-level protocol used to
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communicate with the MySQL database server.
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</para>
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<para>
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By way of an example, the <link linkend="mysqli.overview.pdo">PHP
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Data Objects (PDO)</link> database abstraction layer may use one of
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several database-specific drivers. One of the drivers it has
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available is the PDO MYSQL driver, which allows it to interface with
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the MySQL server.
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</para>
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<para>
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Sometimes people use the terms connector and driver interchangeably,
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this can be confusing. In the MySQL-related documentation the term
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<quote>driver</quote> is reserved for software that provides
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the database-specific part of a connector package.
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</para>
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<para>
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<emphasis role="bold">What is an Extension?</emphasis>
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</para>
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<para>
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In the PHP documentation you will come across another term -
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<emphasis>extension</emphasis>. The PHP code consists of a core,
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with optional extensions to the core functionality. PHP's
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MySQL-related extensions, such as the mysqli
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extension, and the PDO MySQL driver extension, are
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implemented using the PHP extension framework.
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</para>
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<para>
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An extension typically exposes an API to the PHP programmer, to
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allow its facilities to be used programmatically. However, some
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extensions which use the PHP extension framework do not expose an
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API to the PHP programmer.
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</para>
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<para>
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The PDO MySQL driver extension, for example, does not expose an API
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to the PHP programmer, but provides an interface to the PDO layer
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above it.
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</para>
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<para>
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The terms API and extension should not be taken to mean the same
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thing, as an extension may not necessarily expose an API to the
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programmer.
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</para>
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<para>
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<emphasis role="bold">What are the main PHP API offerings for using
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MySQL?</emphasis>
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</para>
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<para>
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There are two main API options when considering connecting to a
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MySQL database server:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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PHP's mysqli Extension
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</para>
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</listitem>
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<listitem>
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<para>
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PHP Data Objects (PDO)
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</para>
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</listitem>
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</itemizedlist>
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<para>
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Each has its own advantages and disadvantages. The following
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discussion aims to give a brief introduction to the key aspects of
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each API.
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</para>
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<para>
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<emphasis role="bold">What is PHP's mysqli Extension?</emphasis>
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</para>
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<para>
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The <literal>mysqli</literal> extension, or as it is sometimes
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known, the MySQL <emphasis>improved</emphasis> extension, was
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developed to take advantage of new features found in MySQL systems
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versions 4.1.3 and newer. The <literal>mysqli</literal> extension is
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included with PHP versions 5 and later.
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</para>
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<para>
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The <literal>mysqli</literal> extension has a number of benefits,
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the key enhancements over the <literal>mysql</literal> extension
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being:
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<itemizedlist>
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<listitem>
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<para>
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Object-oriented interface
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</para>
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</listitem>
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<listitem>
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<para>
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Support for Prepared Statements
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</para>
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</listitem>
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<listitem>
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<para>
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Support for Multiple Statements
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</para>
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</listitem>
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<listitem>
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<para>
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Support for Transactions
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</para>
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</listitem>
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<listitem>
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<para>
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Enhanced debugging capabilities
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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As well as the object-oriented interface the extension also provides
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a procedural interface.
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</para>
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<para>
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The <literal>mysqli</literal> extension is built using the PHP
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extension framework, its source code is located in the directory
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<filename>ext/mysqli</filename>.
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</para>
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<para>
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For further information on the <literal>mysqli</literal> extension,
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see <xref linkend="book.mysqli"/>.
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</para>
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<para xml:id="mysqli.overview.pdo">
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<emphasis role="bold">What is PDO?</emphasis>
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</para>
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<para>
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PHP Data Objects, or PDO, is a database abstraction layer
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specifically for PHP applications. PDO provides a consistent API for
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your PHP application regardless of the type of database server your
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application will connect to. In theory, if you are using the PDO
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API, you could switch the database server you used, from say
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Firebird to MySQL, and only need to make minor changes to your PHP
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code.
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</para>
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<para>
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Other examples of database abstraction layers include JDBC for Java
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applications and DBI for Perl.
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</para>
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<para>
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While PDO has its advantages, such as a clean, simple, portable API,
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its main disadvantage is that it doesn't allow you to use all of the
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advanced features that are available in the latest versions of MySQL
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server. For example, PDO does not allow you to use MySQL's support
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for Multiple Statements.
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</para>
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<para>
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PDO is implemented using the PHP extension framework, its source
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code is located in the directory <filename>ext/pdo</filename>.
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</para>
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<para>
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For further information on PDO, see the
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<xref linkend="book.pdo"/>.
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</para>
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<para>
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<emphasis role="bold">What is the PDO MYSQL driver?</emphasis>
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</para>
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<para>
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The PDO MYSQL driver is not an API as such, at least from the PHP
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programmer's perspective. In fact, the PDO MYSQL driver sits in the
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layer below PDO itself and provides MySQL-specific functionality.
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The programmer still calls the PDO API, but PDO uses the PDO MYSQL
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driver to carry out communication with the MySQL server.
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</para>
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<para>
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The PDO MYSQL driver is one of several available PDO drivers. Other
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PDO drivers available include those for the Firebird and PostgreSQL
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database servers.
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</para>
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<para>
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The PDO MYSQL driver is implemented using the PHP extension
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framework. Its source code is located in the directory
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<filename>ext/pdo_mysql</filename>. It does not expose an API to the
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PHP programmer.
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</para>
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<para>
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For further information on the PDO MYSQL driver, see
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<xref linkend="ref.pdo-mysql"/>.
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</para>
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<para xml:id="mysqli.overview.mysqlnd">
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<emphasis role="bold">What is PHP's MySQL Native Driver?</emphasis>
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</para>
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<para>
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In order to communicate with the MySQL database server, <literal>mysqli</literal> and
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the PDO MYSQL driver each use a low-level library that implements
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the required protocol. In the past, the only available library was
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the MySQL Client Library, otherwise known as
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<literal>libmysqlclient</literal>.
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</para>
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<para>
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However, the interface presented by <literal>libmysqlclient</literal> was
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not optimized for communication with PHP applications, as
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<literal>libmysqlclient</literal> was originally designed with C
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applications in mind. For this reason, the MySQL Native Driver,
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<literal>mysqlnd</literal>, was developed as an alternative to
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<literal>libmysqlclient</literal> for PHP applications.
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</para>
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<para>
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Both, the <literal>mysqli</literal> extension and the PDO MySQL driver can
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each be individually configured to use either
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<literal>libmysqlclient</literal> or <literal>mysqlnd</literal>. As
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<literal>mysqlnd</literal> is designed specifically to be utilised
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in the PHP system it has numerous memory and speed enhancements over
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<literal>libmysqlclient</literal>. You are strongly encouraged to take
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advantage of these improvements.
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</para>
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<para>
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The MySQL Native Driver is implemented using the PHP extension
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framework. The source code is located in
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<filename>ext/mysqlnd</filename>. It does not expose an API to the
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PHP programmer.
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</para>
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<!-- TODO
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<para>
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For further information on the MySQL Native Driver, see
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<xref linkend="book.mysqlnd"/>.
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</para>
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-->
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<para>
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<emphasis role="bold">Comparison of Features</emphasis>
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</para>
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<para>
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The following table compares the functionality of the main
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methods of connecting to MySQL from PHP:
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</para>
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<table xml:id="mysqli.overview.option.comparison">
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<title>Comparison of MySQL API options for PHP</title>
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<tgroup cols="3">
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<colspec colwidth="34*"/>
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<colspec colwidth="33*"/>
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<colspec colwidth="33*"/>
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<thead>
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<row>
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<entry></entry>
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<entry>PHP's mysqli Extension</entry>
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<entry>PDO (Using PDO MySQL Driver and MySQL Native Driver)</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>PHP version introduced</entry>
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<entry>5.0</entry>
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<entry>5.0</entry>
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</row>
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<row>
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<entry>MySQL development status</entry>
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<entry>Active development</entry>
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<entry>Active development</entry>
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</row>
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<row>
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<entry>API supports Charsets</entry>
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<entry>Yes</entry>
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<entry>Yes</entry>
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</row>
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<row>
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<entry>API supports server-side Prepared Statements</entry>
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<entry>Yes</entry>
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<entry>Yes</entry>
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</row>
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<row>
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<entry>API supports client-side Prepared Statements</entry>
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<entry>No</entry>
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<entry>Yes</entry>
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</row>
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<row>
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<entry>API supports Stored Procedures</entry>
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<entry>Yes</entry>
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<entry>Yes</entry>
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</row>
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<row>
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<entry>API supports Multiple Statements</entry>
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<entry>Yes</entry>
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<entry>Most</entry>
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</row>
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<row>
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<entry>Supports all MySQL 4.1+ functionality</entry>
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<entry>Yes</entry>
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<entry>Most</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<!--
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<para>
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<emphasis role="bold">Further information</emphasis>
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</para>
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<para>
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The PHP distribution and documentation are available from the
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<link xlink:href="http://www.php.net/">PHP Web site</link>.
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</para>
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-->
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</chapter>
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