From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jerry Brenner <jbrenner@guidewire.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Why is a sort required for this query? (IS NULL predicate on leading key column)
Date: Wed, 17 Jan 2024 10:11:17 -0500
Message-ID: <2027067.1705504277@sss.pgh.pa.us> (raw)
In-Reply-To: <CACoKFYRfJjpaG+yXAZXdTm7b7UAk4UQwV3-b2H_nmYUMS1TBgA@mail.gmail.com>
References: <CACoKFYRfJjpaG+yXAZXdTm7b7UAk4UQwV3-b2H_nmYUMS1TBgA@mail.gmail.com>
Jerry Brenner <jbrenner@guidewire.com> writes:
> I'm wondering why a sort is required for this query, as the index should be
> providing the required ordering to satisfy the ORDER BY clause. Does it
> have to do with the IS NULL predicate on the leading key column in the
> index?
IS NULL is not seen as an equality condition, no. It's pretty much
of a hack that makes it an indexable condition at all, and we don't
really do any advanced optimization with it.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, jbrenner@guidewire.com, pgsql-performance@lists.postgresql.org
Subject: Re: Why is a sort required for this query? (IS NULL predicate on leading key column)
In-Reply-To: <2027067.1705504277@sss.pgh.pa.us>
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