Re: Small SQL Puzzle

>Consider the following > >select col1, count(*) > from tab1 > group by 1 > having count(*) = 1 >union >select col1, count(*) > from tab2 > group by 1 > having count(*) = 1> >Gives x rows > >Next > >select col1 > from tab1 >union > select col1 > from tab2 >into temp table;> >select col1, count(*) >from temp >having count(*) =1> >gives y rows > >The obvious question is why doesn't x=y? I didn't see the original posting, just someone's reply, and the above may not quote the entire message. Given that, I notice that there is no "group by" clause in the final select statement. What do you get with: select col1, count(*) from temp group by 1 having count(*) = 1; Mark Collins mcollins@us.dhl.com The problem lies in how easily and dangerously we forget that manipulating things is not the same as understanding them.