NULL != 'any Value' evaluates to NULL NULL == 'any Value' evaluates to NULL NULL IS NOT 'any Value' evaluates to TRUE you are looking for the expression testColumn IS NOT 'testValue' to correctly handle NULLs in testColumn
NULL != 'any Value' evaluates to NULL NULL == 'any Value' evaluates to NULL NULL IS NOT 'any Value' evaluates to TRUE you are looking for the expression testColumn IS NOT 'testValue' to correctly handle NULLs in testColumn