Received: from malur.postgresql.org ([217.196.149.56])
	by arkaria.postgresql.org with esmtps  (TLS1.3) tls
 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
	(Exim 4.96)
	(envelope-from <pgsql-hackers-owner+archive@lists.postgresql.org>)
	id 1wxaL3-002r4I-1G
	for pgsql-hackers@arkaria.postgresql.org;
	Sat, 22 Aug 2026 01:16:01 +0000
Received: from localhost ([127.0.0.1] helo=malur.postgresql.org)
	by malur.postgresql.org with esmtp (Exim 4.96)
	(envelope-from <pgsql-hackers-owner+archive@lists.postgresql.org>)
	id 1wxaL2-00FU2u-1H
	for pgsql-hackers@arkaria.postgresql.org;
	Sat, 22 Aug 2026 01:16:00 +0000
Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29])
	by malur.postgresql.org with esmtps  (TLS1.3) tls
 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
	(Exim 4.96)
	(envelope-from <tgl@sss.pgh.pa.us>)
	id 1wxaL2-00FU2l-0K
	for pgsql-hackers@lists.postgresql.org;
	Sat, 22 Aug 2026 01:16:00 +0000
Received: from sss.pgh.pa.us ([68.162.161.243])
	by magus.postgresql.org with esmtps  (TLS1.3) tls
 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
	(Exim 4.98.2)
	(envelope-from <tgl@sss.pgh.pa.us>)
	id 1wxaKy-00000000axu-0BHl
	for pgsql-hackers@lists.postgresql.org;
	Sat, 22 Aug 2026 01:15:59 +0000
Received: from sss1.sss.pgh.pa.us (localhost [127.0.0.1])
	by sss.pgh.pa.us (8.18.1/8.18.1) with ESMTP id 67M1FqSN4122161;
	Fri, 21 Aug 2026 21:15:52 -0400
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Wrong results from join removal with DISTINCT ON + SRF subquery
In-reply-to: 
 <CAMbWs4-hfd1Pyy_zBejsVUSy-3dx16rz2hgUakkKnAg3qg2q=Q@mail.gmail.com>
References: 
 <CAMbWs4-hfd1Pyy_zBejsVUSy-3dx16rz2hgUakkKnAg3qg2q=Q@mail.gmail.com>
Comments: In-reply-to Richard Guo <guofenglinux@gmail.com>
	message dated "Sat, 22 Aug 2026 10:06:33 +0900"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <4122159.1787361352.1@sss.pgh.pa.us>
Date: Fri, 21 Aug 2026 21:15:52 -0400
Message-ID: <4122160.1787361352@sss.pgh.pa.us>
List-Id: <pgsql-hackers.lists.postgresql.org>
List-Help: <https://lists.postgresql.org/manage/>
List-Subscribe: <https://lists.postgresql.org/manage/>
List-Post: <mailto:pgsql-hackers@lists.postgresql.org>
List-Owner: <mailto:pgsql-hackers-owner@lists.postgresql.org>
List-Archive: <https://www.postgresql.org/list/pgsql-hackers>
Archived-At: 
 <https://www.postgresql.org/message-id/4122160.1787361352%40sss.pgh.pa.us>
Precedence: bulk

Richard Guo <guofenglinux@gmail.com> writes:
> Attached is a patch to not rely on DISTINCT ON for distinctness if
> there are any tlist SRFs.  This is more conservative than necessary,
> since the SRFs are only postponed when there is an ORDER BY and none
> of them is in a sort/group column, but I don't think it's worth
> duplicating that logic in analyzejoins.c.

I didn't study the patch in any detail, but I concur with your
thinking here.  SRFs in the tlist are kind of a legacy usage in the
first place, so I don't feel a need to expend lots of effort on
optimizing cases like this.

			regards, tom lane