Re: PostgreSQL query with FULL OUTER JOIN and subquery using column of GROUP BY expression ERROR: subquery uses ungrouped column from outer query

From: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
To: Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
Cc: PALAYRET Jacques <jacques(dot)palayret(at)meteo(dot)fr>, pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Re: PostgreSQL query with FULL OUTER JOIN and subquery using column of GROUP BY expression ERROR: subquery uses ungrouped column from outer query
Date: 2026-02-25 16:20:18
Message-ID: CAKFQuwY27TZSERWdmC+=RO+B86KAOSW+CeJSSL52eUZQLYZsrA@mail.gmail.com
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On Wed, Feb 25, 2026 at 9:00 AM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> 1) Why FROM (SELECT * FROM t1 ) AS t1 instead of just FROM t1?
> Same for JOIN (SELECT * FROM t3 ) t3
>

Seems immaterial. It's just a consequence of simplifying the original
problem query. If it is consequential that would seem buggy.

> 2) Why are the field names not table qualified e.g. t2.id, t3.id, etc?
>

Because of the USING clause, those references shouldn't exist in the main
query.

> 3) What is the desired outcome?
>

For the engine to realize the 'id' in the group by and the 'id' in the
scalar subquery are the same 'id' - the one produced by the USING clause,
not either of the t2 or t3 ids.

My first impression is that this is a bug. Especially since the query
apparently executes in both left-join and right-join modes.

David J.

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