Re: [PATCH] Optimize IS DISTINCT FROM NULL => IS NOT NULL

Marti Raudsepp <marti@juffo.org> writes:
> This patch enables a simple optimization in
> eval_const_expressions_mutator. If we know that one argument to
> DistinctExpr is NULL then we can optimize it to a NullTest, which can
> be an indexable expression.

Uh ... how much do we care about that?  I can't say that I've heard many
people complain about the fact that IS [NOT] DISTINCT FROM is poorly
optimized -- which it is, in general, and this patch chips away at that
only a tiny bit, not enough to make it recommendable.  If we really
wanted to make that a first-class operation we would need far more work
than this.  Plus I don't see why anyone would write the specific case
"IS [NOT] DISTINCT FROM NULL" when they could write half as much.
        regards, tom lane