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(dot)lepikhov(at)postgrespro(dot)ru <mailto:a(dot)lepikhov(at)postgrespro(dot)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