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

On Wed, Nov 10, 2004 at 22:21:31 -0300, Alvaro Herrera <alvherre@dcc.uchile.cl> wrote:
> On Wed, Nov 10, 2004 at 07:18:59PM -0500, Tom Lane wrote:
> 
> > A more radical way of handling it would be to detect the relevance of an
> > indexscan in indxpath.c and generate a special kind of Path node; this
> > would not generalize to other sorts of things as you were hoping, but
> > I'm unconvinced that the mechanism is going to be very general-purpose
> > anyway.  The major advantage is that this would work conveniently for
> > comparing the cost of a rewritten query to a non-rewritten one.
> 
> What about having a new column in pg_aggregate which would point to a
> function that would try to optimize the aggregate's handling?

I think you want to store an operator class and a direction. This allows
you to figure out what indexes might be usable. This could be used
on all of the max and min aggregates and the boolean and and or aggregates.