# ODBC and DB2 Functions (PDO_ODBC)

## Introduction

PDO_ODBC is a driver that implements the PHP Data Objects (PDO) interface to enable access from PHP to databases through ODBC drivers or through the IBM DB2 Call Level Interface (DB2 CLI) library. PDO_ODBC currently supports three different "flavours" of database drivers:

ibm-db2

  Supports access to IBM DB2 Universal Database, Cloudscape, and Apache Derby servers through the free DB2 client.

unixODBC

  Supports access to database servers through the unixODBC driver manager and the database's own ODBC drivers.

generic

  Offers a compile option for ODBC driver managers that are not explicitly supported by PDO_ODBC.

On Windows, PDO_ODBC is built into the PHP core by default. It is linked against the Windows ODBC Driver Manager so that PHP can connect to any database cataloged as a System DSN, and is the recommended driver for connecting to Microsoft SQL Server databases.

## Installation

PDO_ODBC on UNIX systems

1. As of PHP 5.1, PDO_ODBC is included in the PHP source. You can compile the PDO_ODBC extension as either a static or shared module using the following configure commands.

   ibm_db2

         ./configure --with-pdo-odbc=ibm-db2,/opt/IBM/db2/V8.1/

     To build PDO_ODBC with the ibm-db2 flavour, you have to have previously installed the DB2 application development headers on the same machine on which you are compiling PDO_ODBC. The DB2 application development headers are an installable option in the DB2 servers, and are also available as part of the DB2 Application Development Client freely available for download from the IBM DB2 Universal Database » support site.

     If you do not supply a location for the DB2 libraries and headers to the configure command, PDO_ODBC defaults to /home/db2inst1/sqllib.

   unixODBC

         ./configure --with-pdo-odbc=unixODBC,/usr/local

     If you do not supply a location for the unixODBC libraries and headers to the configure command, PDO_ODBC defaults to /usr/local.
   generic

         ./configure --with-pdo-odbc=generic,/usr/local,libname,ldflags,cflags

## Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

PDO_ODBC Configuration Options
Name | Default | Changeable | Changelog
--- | --- | --- | ---
pdo_odbc.connection_pooling | "strict" | PHP_INI_ALL | Available since PHP 5.1.0.
pdo_odbc.db2_instance_name | NULL | PHP_INI_SYSTEM | Available since PHP 5.1.1. Removed in PHP 6.0.0.

For further details and definitions of the PHP_INI_* constants, see the php.ini directives.

Here's a short explanation of the configuration directives.

`pdo_odbc.connection_pooling` string

  Whether to pool ODBC connections. Can be one of "strict", "relaxed" or "off" (equals to ""). The parameter describes how strict the connection manager should be when matching connection parameters to existing pooled connections. `strict` is the recommend default, and will result in the use of cached connections only when all the connection parameters match exactly. `relaxed` will result in the use of cached connections when similar connection parameters are used. This can result in increased use of the cache, at the risk of bleeding connection information between (for example) virtual hosts.

  This setting can only be changed from the php.ini file, and affects the entire process; any other modules loaded into the process that use the same ODBC libraries will be affected too, including the Unified ODBC extension.

  Warning

  `relaxed` matching should not be used on a shared server, for security reasons.

  Tip

  Leave this setting at the default `strict` setting unless you have good reason to change it.

`pdo_odbc.db2_instance_name` string

  If you compile PDO_ODBC using the db2 flavour, this setting sets the value of the DB2INSTANCE environment variable on Linux and UNIX operating systems to the specified name of the DB2 instance. This enables PDO_ODBC to resolve the location of the DB2 libraries and make cataloged connections to DB2 databases.

  This setting can only be changed from the php.ini file, and affects the entire process; any other modules loaded into the process that use the same ODBC libraries will be affected too, including the Unified ODBC extension.

  This setting has no effect on Windows.