From: Tom Lane <tgl@sss.pgh.pa.us>
To: Eric Ridge <eebbrr@gmail.com>
cc: pgsql-general <pgsql-general@postgresql.org>,
        Richard Guo <guofenglinux@gmail.com>
Subject: Re: pg18 bug? SELECT query doesn't work
In-reply-to: <C7FCAD3A-9859-4CCB-95DE-62ECF1368331@gmail.com>
References: <7900964C-F99E-481E-BEE5-4338774CEB9F@gmail.com> <C7FCAD3A-9859-4CCB-95DE-62ECF1368331@gmail.com>
Comments: In-reply-to Eric Ridge <eebbrr@gmail.com>
	message dated "Tue, 06 Jan 2026 10:52:56 -0500"
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Date: Tue, 06 Jan 2026 13:52:12 -0500
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Eric Ridge <eebbrr@gmail.com> writes:
> Here's an even more reduced test case.  No tables or data:

> # SELECT * FROM (SELECT upper(unnest(ARRAY['cat', 'dog'])) as animal FRO=
M generate_series(1, 10) GROUP BY 1) x WHERE animal ilike 'c%';

> pg15 returns:

>  animal  =

> --------
>  CAT
> (1 row)

> and pg18 says:

> # SELECT * FROM (SELECT upper(unnest(ARRAY['cat', 'dog'])) as animal FRO=
M generate_series(1, 10) GROUP BY 1) x WHERE animal ilike 'c%';
> ERROR:  set-valued function called in context that cannot accept a set
> LINE 1: SELECT * FROM (SELECT upper(unnest(ARRAY['cat', 'dog'])) as ...
>                                     ^

I agree that this is a bug.  "git bisect" says it broke at

247dea89f7616fdf06b7272b74abafc29e8e5860 is the first bad commit
commit 247dea89f7616fdf06b7272b74abafc29e8e5860 (HEAD)
Author: Richard Guo <rguo@postgresql.org>
Date:   Tue Sep 10 12:35:34 2024 +0900

    Introduce an RTE for the grouping step
    =

I've not probed further than that, but my guess is that now we check
for set-returning tlist items while the tlist still has grouping Vars,
thus missing the fact that there's a SRF represented by one of those
Vars.  This prompts us to flatten a subquery we shouldn't have
flattened (because that ends by introducing a SRF into the outer
WHERE).

			regards, tom lane