SQL check in XOR

Hi to all, I have more SQL in which check for accounting infos. In my "sites-enabled/default" file I have in my accounting section: {... sql1 sql2 sql3 ... } I notice that in this way the process check if AT LEAST one of above tables "returns ok", but I'd want accounting module returns OK iff exactly ONE of that returns ok. Is there a way to configure in this XOR way? Thanks in advance. Regards -- Rosario L.