Message-ID: <e7f740cd-fcc8-4022-bb12-bb0f5f736ba6@postgrespro.ru>
Date: Thu, 9 Nov 2023 11:51:14 +0700
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Subject: Re: BUG #18187: Unexpected error: "variable not found in subplan
 target lists" triggered by JOIN
To: Richard Guo <guofenglinux@gmail.com>
Cc: zuming.jiang@inf.ethz.ch, pgsql-bugs@lists.postgresql.org,
 PG Bug reporting form <noreply@postgresql.org>
References: <18187-831da249cbd2ff8e@postgresql.org>
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 <CAMbWs4_yrqMYXd+zXc4Y6KjnyA8xPZE6aiAW6k2Y10WaNhwRhw@mail.gmail.com>
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From: Andrei Lepikhov <a.lepikhov@postgrespro.ru>
Organization: Postgres Professional
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On 9/11/2023 10:54, Richard Guo wrote:
> 
> On Wed, Nov 8, 2023 at 11:42 PM Andrei Lepikhov 
> <a.lepikhov@postgrespro.ru <mailto:a.lepikhov@postgrespro.ru>> wrote:
> 
>     The issue looks like previous one, related to new SJE feature.
> 
>     Reduced case:
>     CREATE TABLE t2 (vkey int4, c9 text, primary key(vkey));
>     SELECT * FROM (
>         SELECT CASE WHEN '1' = ref_0.c9 THEN 1 ELSE 1 END AS c_3
>     FROM t2 as ref_0
>         JOIN t2 AS ref_1
>         ON ref_0.vkey = ref_1.vkey
>           RIGHT OUTER JOIN t2 AS ref_2
>           ON ref_1.vkey = ref_2.vkey) AS t5
>         RIGHT OUTER JOIN (SELECT 1 AS c_2) AS t4
>         ON t4.c_2 IS NOT NULL;
> 
>     The key problem lies in the 'CASE' statement.
> 
> 
> I've looked into this a little bit.  I think it's caused by the SJE
> logic not properly removing references from PHVs.  Specifically, it
> fails to replace the ref_0's Vars within phv->phexpr, leading them to be
> added in ref_2/ref_1 join's targetlist.
> 
> Also, I noticed that in remove_rel_from_query() we perform replace_relid
> for phv->phrels twice at line 475 and 478, which seems not right to me.
> 
>   475   phv->phrels = replace_relid(phv->phrels, relid, subst);
>   476   phv->phrels = replace_relid(phv->phrels, ojrelid, subst);
>   477   phinfo->ph_lateral = replace_relid(phinfo->ph_lateral, relid, 
> subst);
>   478   phinfo->ph_var->phrels = replace_relid(phinfo->ph_var->phrels, 
> relid, subst);

Thanks a lot!
Your patch looks correct. We really have been missing replacing the 
PlaceHolderVar expression references for all the development time.
The test in join.sql works correctly. Should we add a reference to the 
bug that triggered the issue as a comment to the test? Also, to be sure, 
maybe add column t4.code into the list of the coalesce parameters?

-- 
regards,
Andrei Lepikhov
Postgres Professional