Stephan Szabo <sszabo@megazone23.bigpanda.com> writes:
> Actually, hadn't we figured that pushing to the left side of except was
> safe?
It's not safe for EXCEPT ALL (you might get the wrong number of
duplicates out), and I'm not entirely convinced about EXCEPT.
Also, the point of pushing down is to speed up the subqueries, so I'm
not sure there's much win if you can't push to both sides.
All in all I'd just as soon leave the EXCEPT case alone.
regards, tom lane