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From: Alexander Lakhin <exclusion@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18953: Planner fails to build plan for complex query with LATERAL references
Date: Sat, 28 Jun 2025 09:00:01 +0300
Message-ID: <6072cd36-8d7b-457a-a7c6-7cf41c05fe6c@gmail.com> (raw)
In-Reply-To: <2075249.1751060239@sss.pgh.pa.us>
References: <18953-1c9883a9d4afeb30@postgresql.org>
	<CAMbWs49XTfPD9OCw9xWsRtbiNYgQ-Nau_hHy9UbbGP-w2V=ANQ@mail.gmail.com>
	<1268645.1749765012@sss.pgh.pa.us>
	<1499514.1749848324@sss.pgh.pa.us>
	<CAMbWs4_E7wC3LX17jr+RnRunz9ROcwhn0eXt0riJ6FjbxB0g+g@mail.gmail.com>
	<527134.1750087495@sss.pgh.pa.us>
	<CAMbWs4_wYvQWHCwBfSXj9OQ-fWn+xnntR+EVzks2KB0eRWcRpw@mail.gmail.com>
	<835659.1750177751@sss.pgh.pa.us>
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	<1487176.1750963077@sss.pgh.pa.us>
	<CAMbWs4_iW1e5ciQN1U7a8Nz773D5cV3p6UrL2zeXrbhoqzr=iw@mail.gmail.com>
	<2056150.1751049350@sss.pgh.pa.us>
	<2075249.1751060239@sss.pgh.pa.us>

Hello Tom and Richard,

28.06.2025 00:37, Tom Lane wrote:
> ... BTW, looking at these two patches again, I wonder if it'd be
> better to put the hackery for SubLink conversion into
> identify_current_nestloop_params?  That'd remove the need to argue
> that we don't have to fix both copies of a nestloop-parameter PHV.
> The responsibility doesn't clearly belong to
> identify_current_nestloop_params, but it doesn't clearly belong
> to create_nestloop_plan either, so neither choice seems superior
> from a modularity standpoint.

I've discovered a query which fails with an error after a16ef313f with
both v2 patches applied:
create temp table t(i int primary key);
select * from
     (select k from
         (select i, coalesce(i, j) as k from
             (select i from t union all select 1)
             join (select 1 as j limit 1) on i = j)
         right join (select 1) on true
         join (select 1) on i is not null
     ),
     lateral (select k offset 1);
ERROR:  XX000: variable not found in subplan target list
LOCATION:  fix_upper_expr_mutator, setrefs.c:3310

Thank you for working on this!

Best regards,
Alexander

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