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help / color / mirror / Atom feedFrom: Tom Lane <[email protected]>
To: jian he <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Cc: Richard Guo <[email protected]>
Subject: Re: JumbleQuery ma treat different GROUP BY expr as the same
Date: Sat, 10 Jan 2026 11:46:27 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CACJufxEy2W+tCqC7XuJ94r3ivWsM=onKJp94kRFx3hoARjBeFQ@mail.gmail.com>
References: <CACJufxEy2W+tCqC7XuJ94r3ivWsM=onKJp94kRFx3hoARjBeFQ@mail.gmail.com>
jian he <[email protected]> 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->groupexprs 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=# 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 by a
1 | 0 | explain(costs off, verbose) select count(*) from t group by b
1 | 0 | explain(costs off, verbose) select count(*) from t group by c
(4 rows)
So I'm inclined to think this was an unintentional change of behavior.
regards, tom lane
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