Re: BUG #18187: Unexpected error: "variable not found in subplan target lists" triggered by JOIN

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