"Evan D. Hoffman" <evandhoffman@gmail.com> writes:
> Because we have both 9.0 and 9.1 running, and a query that succeeds
> under 9.1 was failing under 9.0. Can I assume the answer then is
> "no"?
There are any number of reasons a query might work in version N and not
in N-1. If you've got requirements like that, you should be developing
on the oldest version you're worried about supporting ...
regards, tom lane