"Tomas Vondra" <tv@fuzzy.cz> writes:
> Could the planner do this reasoning, i.e. see if there's a NOT NULL
> constraint on the column and change the plan accordingly?
Possibly. I'm not sure how expensive it would be. Right now, a
structural change of that sort would have to be done pretty early in
planning, and we don't have a lot of info collected about the tables
at that point. I'm afraid it would involve a special-purpose catalog
probe, which would add a lot of overhead.
regards, tom lane