From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: Kaimeh <kkaimeh@gmail.com>, pgsql-bugs@lists.postgresql.org
Subject: Re: Error when using array_agg with filter where clause in pg16 and
 pg17
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Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Wed, 09 Apr 2025 11:55:55 +1200"
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Date: Tue, 08 Apr 2025 20:25:54 -0400
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David Rowley <dgrowleyml@gmail.com> writes:
> On Wed, 9 Apr 2025 at 03:32, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> The simplest fix I can think of is to disable the presorted-agg
>> optimization if (1) there's a FILTER clause and (2) the proposed
>> sort key is anything more complex than a Var.

> Unfortunately, the situation is a little worse than what you
> highlighted, as I think I didn't consider FILTER at all, and this
> means I didn't consider the costing differences between filtering then
> sorting vs sorting then filtering.

Oooh.  If the FILTER clause is selective, that could easily mean that
the "optimization" loses big from having to sort many more tuples.
I wonder if we should just not apply it when there's a FILTER,
full stop.

			regards, tom lane