Re: execution plan is wrong, or the query ?

Alex Burkoff <alex.burkoff@jivesoftware.com> writes:
> I have a following query that used to work as intended on 8.3.5 :
> ...
> After upgrade to 9.2 the query doesn't return the same results any more, and the execution plan has changed :

You'd need to provide a self-contained test case if you want an informed
opinion on this.  The odds that 8.3.5 was wrong and the newer result is
right are not negligible.  (If you were comparing to a *current* 8.3
release I might be more prepared to assume that 9.2 is the one that is
broken.)

FWIW, it looks like the 9.2 plan has been simplified by outer-join
elimination, which implies that unique constraints on the join columns
matter.  Possibly you've found a bug in that optimization, but without
a concrete test case it's impossible to be sure, let alone fix it.

            regards, tom lane