From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
cc: holger.reise@vitagroup.ag, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18284: Filter in left lateral join not respected
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Comments: In-reply-to Richard Guo <guofenglinux@gmail.com>
	message dated "Fri, 12 Jan 2024 14:50:33 +0800"
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Date: Fri, 12 Jan 2024 09:59:39 -0500
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Richard Guo <guofenglinux@gmail.com> writes:
> On Fri, Jan 12, 2024 at 1:30 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Somehow that didn't cause any visible
>> problems before 4be058fe9, or more likely we just didn't get any
>> relevant trouble reports.

> I believe it should be the latter case.  It's not hard to show this
> problem before 4be058fe9.

> create table t (a int);
> insert into t values (1);

> # select t2a_lateral from t t1
>     left join (select coalesce(t2.a) as a from t t2) s on true
>     left join lateral (select s.a as t2a_lateral from t t3) ss on false;
>  t2a_lateral
> -------------
>            1
> (1 row)

Ah, of course.  The previous test case had FROM-less subselects,
so prior to 4be058fe9 we couldn't flatten those and the bug didn't
manifest.  But with ordinary FROM clauses, boom!

Now I'm fairly astonished that this was never reported before.
You'd think in ten years somebody would've noticed.

			regards, tom lane