Message-ID: <60c6b1f7-f435-4ca7-992a-482417af5130@gmail.com>
Date: Fri, 4 Sep 2026 17:12:20 +0200
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Subject: Re: BUG #19649: Qual pushdown into GROUP BY subqueries ignores
 non-equivalence-preserving references to grouping col
To: Andrey Rachitskiy <pl0h0yp1@gmail.com>, 303677365@qq.com,
 pgsql-bugs@lists.postgresql.org
Cc: Tender Wang <tndrwang@gmail.com>
References: <19649-2cabf1440793cc71@postgresql.org>
 <CAB8bMiss5S2SZonboQfbTMJsNCd+k_J8AbeS-vXheVUrR_TUhQ@mail.gmail.com>
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From: Andrei Lepikhov <lepihov@gmail.com>
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On 03/09/2026 23:17, Andrey Rachitskiy wrote:
> This blocks wrapper-based finer equivalence at pushdown boundaries while
> preserving existing behavior for truly direct operands.
I don't like this fix. It causes regressions where we haven't had it before.
Let's see:

CREATE TABLE r(i int, s text, ts timestamptz);
EXPLAIN (COSTS OFF)
SELECT * FROM (SELECT i, count(*) c FROM r GROUP BY i) s WHERE i::text = '5';

Before:

 GroupAggregate
   Group Key: r.i
   ->  Sort
         Sort Key: r.i
         ->  Seq Scan on r
               Filter: ((i)::text = '5'::text)

With your fix:

 HashAggregate
   Group Key: r.i
   Filter: ((r.i)::text = '5'::text)
   ->  Seq Scan on r

I think, filter should be pushed down to the scan.

-- 
regards, Andrei Lepikhov,
pgEdge