From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: ganeshmmahesh@gmail.com, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #17068: Incorrect ordering of a particular row.
Date: Tue, 22 Jun 2021 10:00:22 -0400
Message-ID: <1714546.1624370422@sss.pgh.pa.us> (raw)
In-Reply-To: <CAApHDvoKk=NO7H6p8UNjSXbio8vq9yUjZhHO_Xr=C14WMs9i+A@mail.gmail.com>
References: <17068-18d0626f1d26394d@postgresql.org>
<CAApHDvr=A5ZMYm-Jy1g4AyfMBeOJGfP_5zJEW9N9k_S5PjwN4Q@mail.gmail.com>
<CA+hUKG+TrnLnccaspLsimQnm34wUsdxSpxQiS9jrTScUo=kFiQ@mail.gmail.com>
<CAApHDvoKk=NO7H6p8UNjSXbio8vq9yUjZhHO_Xr=C14WMs9i+A@mail.gmail.com>
David Rowley <dgrowleyml@gmail.com> writes:
> On Wed, 23 Jun 2021 at 01:26, Thomas Munro <thomas.munro@gmail.com> wrote:
>> If you change the SELECT list to output alias3::text, there's a
>> different value there:
> Yeah, if I change it to ORDER BY alias3.lastname, nullnamesb.id;
> instead of ORDER BY alias3.*, nullnamesb.id; then the tie break using
> btint4fastcmp() is called more often. It's also getting called with
> the missing 4s which I mentioned upthread.
> See the two outputs. That points me towards something weird going on
> in record_cmp().
I believe Munro's point is that in some rows alias3.* is a NULL composite
value, while in other rows it is a composite containing one NULL, and they
don't sort the same. Presumably the former are from left-join extension
while the latter come from actual table rows having NULL in that column.
(I'd suspected something of the kind, but being caffeine-deprived I'd
first added "alias3.* IS NULL" to the query, which of course fails to
expose the difference. Thanks SQL.)
In short, I see no bug here. It is kind of obscure though.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, dgrowleyml@gmail.com, thomas.munro@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17068: Incorrect ordering of a particular row.
In-Reply-To: <1714546.1624370422@sss.pgh.pa.us>
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