From: Tom Lane <tgl@sss.pgh.pa.us>
To: jian he <jian.universality@gmail.com>
cc: PostgreSQL-development <pgsql-hackers@postgresql.org>,
        Richard Guo <guofenglinux@gmail.com>
Subject: Re: JumbleQuery ma treat different GROUP BY expr as the same
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References: <CACJufxEy2W+tCqC7XuJ94r3ivWsM=onKJp94kRFx3hoARjBeFQ@mail.gmail.com>
Comments: In-reply-to jian he <jian.universality@gmail.com>
	message dated "Sat, 10 Jan 2026 21:13:39 +0800"
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Date: Sat, 10 Jan 2026 11:46:27 -0500
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jian he <jian.universality@gmail.com> writes:
> explain(costs off, verbose) select count(*) from t group by a;
> explain(costs off, verbose) select count(*) from t group by b;
> explain(costs off, verbose) select count(*) from t group by c;

> JumbleQuery will jumble Query->groupClause, but RangeTblEntry->groupexpr=
s in
> Query->rtable is marked with query_jumble_ignore and therefore excluded =
from
> jumbling.

> So  "group by a" and "group by" merged into the same entry in
> pg_stat_statements,
> Is this what we expected?

It is not what happened before we invented RTE_GROUP.  I tried your
experiment in v14 and got:

regression=3D# SELECT calls, rows, query FROM pg_stat_statements ORDER BY =
query COLLATE "C";
 calls | rows |                             query                         =
    =

-------+------+-----------------------------------------------------------=
----
     1 |    1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
     1 |    0 | explain(costs off, verbose) select count(*) from t group b=
y a
     1 |    0 | explain(costs off, verbose) select count(*) from t group b=
y b
     1 |    0 | explain(costs off, verbose) select count(*) from t group b=
y c
(4 rows)

So I'm inclined to think this was an unintentional change of behavior.

			regards, tom lane