Re: Proving IS NOT NULL inference for ScalarArrayOpExpr's

On Tue, Jan 22, 2019 at 4:26 AM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
>
> Hello, I gave this patch a very quick scan.  I didn't check the actual
> logic behind it.
>
> This comment seems wrong:
>
> + * However weak implication fails: e.g., "NULL IS NOT NULL" is false, but
> + * "NULL = ANY(ARRAY[NULL])" is NULL, so non-falsity does not imply non-falsity.
>
> "non-falsity does not imply non-falsity"?  I suppose one of those
> negations should be different ...

Earlier in the file weak implication (comments above
predicate_implied_by) is defined as "non-falsity of A implies
non-falsity of B". In this example we have NULL for A (non-false) but
false for B, so that definition doesn't hold. So I think the comment
is accurate, but I can reword if you have an idea of what you'd like
to see (I've tweaked a bit in the attached patch to start).

> I think the name clause_proved_for_null_test() is a bit weird, being in
> the past tense.  I'd maybe change "proved" to "proves".

Changed.

> s/exppresions/expresions/ in the test files.

Fixed.

James Coleman