Re: BUG #17068: Incorrect ordering of a particular row.

David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> On Wed, 23 Jun 2021 at 01:26, Thomas Munro <thomas(dot)munro(at)gmail(dot)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