Re: Proving IS NOT NULL inference for ScalarArrayOpExpr's

From: James Coleman <jtc331(at)gmail(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Proving IS NOT NULL inference for ScalarArrayOpExpr's
Date: 2019-01-22 15:49:29
Message-ID: CAAaqYe-yvGTdNaJ2xcjmN4hykaqFSBd2bSd2EZ-Z4auUy7owuA@mail.gmail.com
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> > 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 forgot to update in v8 so attaching v9.

James Coleman

Attachment Content-Type Size
saop_is_not_null-v9.patch application/octet-stream 26.2 KB

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