PHP Manual: PDO

The PDO_ODBC Data Source Name (DSN) is composed of the following elements:

DSN prefix: The DSN prefix is odbc:. If you are connecting to a database cataloged in the ODBC driver manager or the DB2 catalog, you can append the cataloged name of the database to the DSN.
DSN: The name of the database as cataloged in the ODBC driver manager or the DB2 catalog. Alternately, you can provide a complete ODBC connection string to connect to a database as described at » https://www.connectionstrings.com/.
UID: The name of the user for the connection. If you specify the user name in the DSN, PDO ignores the value of the user name argument in the PDO constructor.
PWD: The password of the user for the connection. If you specify the password in the DSN, PDO ignores the value of the password argument in the PDO constructor.

Version	Description
8.4.0	When passing an empty string to the password argument in the PDO constructor, `pwd` was not included in the connection string created until now, but the behavior has been changed to include it as an empty string. Passing `null` for the password argument in the PDO constructor results in the same behavior as before.
8.4.0	Changed the behavior to ignore the user name argument and the password argument in the PDO constructor separately when the DSN contains `uid` or `pwd`. Previously, if included only either `uid` or `pwd` in the DSN, both the user name argument and the password argument in the PDO constructor were ignored.

Example #1 PDO_ODBC DSN example (ODBC driver manager)

The following example shows a PDO_ODBC DSN for connecting to an ODBC database cataloged as testdb in the ODBC driver manager:

odbc:testdb

Example #2 PDO_ODBC DSN example (IBM DB2 uncataloged connection)

The following example shows a PDO_ODBC DSN for connecting to an IBM DB2 database named SAMPLE using the full ODBC DSN syntax:

odbc:DRIVER={IBM DB2 ODBC DRIVER};HOSTNAME=localhost;PORT=50000;DATABASE=SAMPLE;PROTOCOL=TCPIP;UID=db2inst1;PWD=ibmdb2;

Example #3 PDO_ODBC DSN example (Microsoft Access uncataloged connection)

The following example shows a PDO_ODBC DSN for connecting to a Microsoft Access database stored at C:\db.mdb using the full ODBC DSN syntax:

odbc:Driver={Microsoft Access Driver (*.mdb)};Dbq=C:\\db.mdb;Uid=Admin