In MFC 4.2, CDatabase::SetSynchronousMode became obsolete.
The MFC ODBC classes now use only synchronous processing. To start an asychronous operation, you must directly call the ODBC API function SQLSetConnectOption. For more information, see the topic "Executing Functions Asynchronously" in the Windows SDK.
Although SetSynchronousMode is obsolete, your code will still compile if you use this member function. SetSynchronousMode will simply generate a TRACE message that it is doing nothing.