Re: Useless sort by

Gaetano Mendola <mendola(at)gmail(dot)com> writes:
> Of course I'm not suggesting to take away the "sort by" and give the user
> an unsorted result, I'm asking why the the optimizer in cases like:

> select unique(a) from v_table_with_order_by;

> doesn't takes away the "order by" inside the view and puts it back "rewriting the
> query like this:

> select unique(a) from v_table_without_order_by
> order by a;

That changes the order in which the rows are fed to unique(a). The
principal real-world use for a non-top-level ORDER BY is exactly to
determine the order in which rows are fed to a function, so we will
have a revolt on our hands if we break that.

regards, tom lane