Re: efficiency of group by 1 order by 1

"Merlin Moncure" <mmoncure@gmail.com> writes:
> select f(x) from t where id = 1 order by n;
> can cause f to execute for the entire table even if id is unique.

Really?  I'd consider it a bug if so.  Compare

    select 1/x from t where x > 0

If the presence of zeroes in t can make this throw a zero-divide error,
the database is broken.  In my mind the SQL spec is perfectly clear that
WHERE filtering occurs before evaluation of the SELECT targetlist.
(Sorting, however, occurs afterward --- so there are certainly potential
gotchas of this ilk.  But the specific example you give is bogus.)

            regards, tom lane