 <p>this worked for me :)</p> <blockquote> <p>select * from Common </p> <p>where </p> <p>common_id not in (select <strong>ISNULL(common_id,'dummy-data')</strong> from Table1)</p> <p>and common_id not in (select <strong>ISNULL(common_id,'dummy-data')</strong> from Table2)</p> </blockquote>