"Tomas Vondra" <t...@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

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