David Rowley wrote: > > Would it be very difficult to extend that to "if any unique constraints are > > contained in the DISTINCT clause"? > > Unfortunately, it's quite a bit more work to make that happen. It's > not just unique constraints that are required to make this work. We > also need to pay attention to NOT NULL constraints too, as we're > unable to prove function dependency when the keys have NULLs, as there > may be any number of rows containing NULL values. > > The problem is that in order to properly invalidate cached plans we > must record the constraint OIDs which the plan depends on. We can do > that for PK and UNIQUE constraints, unfortunately, we can't do it for > NOT NULL constraints as, at the moment, these are just properties of > pg_attribute. For this to be made to work we'd need to store those in > pg_constraint too, which is more work that I'm going to do for this > patch.
That makes sense; thanks for explaining. Yours, Laurenz Albe
