Sets the transaction
If optional and not specified, the function will try to find an open link to the FrontBase server and if no such link is found it will try to create one as if fbsql_connect() was called with no arguments
The type of locking to be set. It can be one of the following constants: FBSQL_LOCK_DEFERRED, FBSQL_LOCK_OPTIMISTIC, or FBSQL_LOCK_PESSIMISTIC.
The type of isolation to be set. It can be one of the following constants: FBSQL_ISO_READ_UNCOMMITTED, FBSQL_ISO_READ_COMMITTED, FBSQL_ISO_REPEATABLE_READ, FBSQL_ISO_SERIALIZABLE, or FBSQL_ISO_VERSIONED.