php--PDO introduction and installation configuration

Introduction

The PHP Data Objects (PDO) extension defines a lightweight, consistent interface for PHP to access databases. Each database driver that implements the PDO interface can expose database-specific features as standard extensions. Note that using PDO extensions by itself does not implement any database functionality; a database-specific PDO driver must be used to access database services.

PDO provides a data access abstraction layer, which means that no matter which database is used, the same functions (methods) can be used to query and obtain data. PDO does not provide a database abstraction layer; it does not rewrite SQL and does not emulate missing features. If necessary, a mature abstraction layer should be used.

PDO has been included since PHP 5.1, and is used as a PECL extension in PHP 5.0. PDO requires new features of PHP 5 core and therefore will not run on older versions of PHP.

Installation Configuration

Installing PDO on Unix systems

Since PHP 5.1.0, PDO and PDO_SQLITE drivers are available by default. For the database of your choice, you need to enable the corresponding POD driver;

Note:

When building PDO with shared extensions (not recommended), all PDO drivers must be loaded after PDO itself.

When installing PDO as a shared module, you need to update the php.ini file so that the PDO extension is automatically loaded when PHP is run. Specific database drivers also need to be enabled there; make sure they are listed after the pdo.so line, as PDO must be initialized before the specific database extensions can be loaded. If you are building PDO and database-specific extensions statically, you can skip this step.

extension=pdo.so

Windows environment

PDO and all major drivers are distributed with PHP as shared extensions, to activate them simply edit the php.ini file:

extension=php_pdo.dll

Note:

This step is available in PHP 5.3 and above Not required in later versions, for PDO no longer needs to be a DLL file.

Next step, select other database-specific DLL files, and then either load them with dl() at runtime, or enable them behind php_pdo.dll in php.ini. For example:

extension=php_pdo.dll
extension=php_pdo_firebird.dll
extension=php_pdo_informix.dll
extension=php_pdo_mssql.dll
extension=php_pdo_mysql.dll
extension=php_pdo_oci.dll
extension=php_pdo_oci8.dll
extension=php_pdo_odbc.dll
extension=php_pdo_pgsql.dll
extension=php_pdo_sqlite.dll

Those DLL files should exist in the system’s extension_dir.

Note:

Remember: After changing the php.ini file, you need to restart the PHP service for the new configuration instructions to take effect.