MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 17: Programming Considerations
When an ODBC 3.x application calls SQLGetDiagField in an ODBC 2.x driver, the driver will return SQL_SUCCESS and the appropriate information in *DiagInfoPtr if the DiagIdentifier argument is SQL_DIAG_CLASS_ORIGIN, SQL_DIAG_CLASS_SUBCLASS_ORIGIN, SQL_DIAG_CONNECTION_NAME, SQL_DIAG_MESSAGE_TEXT, SQL_DIAG_NATIVE, SQL_DIAG_NUMBER, SQL_DIAG_RETURNCODE, SQL_DIAG_SERVER_NAME, or SQL_DIAG_SQLSTATE. All other diagnostic fields will return SQL_ERROR.