Re: Small SQL Puzzle

On Thu, 26 Feb 1998 11:32:24 +0000, Paul Watson <watson@mcmail.com> wrote: >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? Because the second union eliminates duplicates from BOTH tab1 and tab2 together, rather than just dups from tab1 then dups from tab2. I would expect that x >= y, right? Karl