&reftitle.constants; &pdo.driver-constants;

`PDO::SQLSRV_TXN_READ_UNCOMMITTED` (`int`)

- This constant is an acceptable value for the SQLSRV DSN key TransactionIsolation. This constant sets the transaction isolation level for the connection to Read Uncommitted.

`PDO::SQLSRV_TXN_READ_COMMITTED` (`int`)

- This constant is an acceptable value for the SQLSRV DSN key TransactionIsolation. This constant sets the transaction isolation level for the connection to Read Committed.

`PDO::SQLSRV_TXN_REPEATABLE_READ` (`int`)

- This constant is an acceptable value for the SQLSRV DSN key TransactionIsolation. This constant sets the transaction isolation level for the connection to Repeateable Read.

`PDO::SQLSRV_TXN_SNAPSHOT` (`int`)

- This constant is an acceptable value for the SQLSRV DSN key TransactionIsolation. This constant sets the transaction isolation level for the connection to Snapshot.

`PDO::SQLSRV_TXN_SERIALIZABLE` (`int`)

- This constant is an acceptable value for the SQLSRV DSN key TransactionIsolation. This constant sets the transaction isolation level for the connection to Serializable.

`PDO::SQLSRV_ENCODING_BINARY` (`int`)

- Specifies that data is sent/retrieved as a raw byte stream to/from the server without performing encoding or translation. This constant can be passed to PDOStatement::setAttribute, PDO::prepare, PDOStatement::bindColumn, and PDOStatement::bindParam.

`PDO::SQLSRV_ENCODING_SYSTEM` (`int`)

- Specifies that data is sent/retrieved to/from the server as 8-bit characters as specified in the code page of the Windows locale that is set on the system. Any multi-byte characters or characters that do not map into this code page are substituted with a single byte question mark (?) character. This constant can be passed to PDOStatement::setAttribute, PDO::setAttribute, PDO::prepare, PDOStatement::bindColumn, and PDOStatement::bindParam.

`PDO::SQLSRV_ENCODING_UTF8` (`int`)

- Specifies that data is sent/retrieved to/from the server in UTF-8 encoding. This is the default encoding. This constant can be passed to PDOStatement::setAttribute, PDO::setAttribute, PDO::prepare, PDOStatement::bindColumn, and PDOStatement::bindParam.

`PDO::SQLSRV_ENCODING_DEFAULT` (`int`)

- Specifies that data is sent/retrieved to/from the server according to PDO::SQLSRV_ENCODING_SYSTEM if specified during connection. The connection's encoding is used if specified in a prepare statement. This constant can be passed to PDOStatement::setAttribute, PDO::setAttribute, PDO::prepare, PDOStatement::bindColumn, and PDOStatement::bindParam.

`PDO::SQLSRV_ATTR_QUERY_TIMEOUT` (`int`)

- A non-negative integer representing the timeout period, in seconds. Zero (0) is the default and means no timeout. This constant can be passed to PDOStatement::setAttribute, PDO::setAttribute, and PDO::prepare.

`PDO::SQLSRV_ATTR_DIRECT_QUERY` (`int`)

- Indicates that a query should be executed directly, without being prepared. This constant can be passed to PDO::setAttribute, and PDO::prepare. For more information, see Direct and Prepared Statement Execution.