Re: MAX/MIN optimization via rewrite (plus query rewrites generally)

On Thu, Nov 11, 2004 at 10:24:34 -0500,
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> We know how to determine that an index matches an ORDER BY clause.
> But what has an aggregate called MAX() got to do with ORDER BY? Magic
> assumptions about operators named "<" are not acceptable answers; there
> has to be a traceable connection in the catalogs.
>
> As a real-world example of why I won't hold still for hard-wiring this:
> a complex-number data type might have btree opclasses allowing it to be
> sorted either by real part or by absolute value. One might then define
> max_real() and max_abs() aggregates on the type. It should be possible
> to optimize such aggregates the same way as any other max() aggregate.

Wouldn't knowing an opclass and direction associated with an aggregrate
function allow you to do this?