PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> Wouldn't it be good to push order by clause even when where clause is given
> in query?
Maybe, but you haven't demonstrated it. In the example you show,
the query plan still requires a local sort, so pre-sorting the
individual inputs to that would just add cycles without accomplishing
anything.
In any case, this is not a bug.
regards, tom lane