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From: jian he <jian.universality@gmail.com>
Date: Sat, 10 Jan 2026 21:13:39 +0800
Message-ID: <CACJufxEy2W+tCqC7XuJ94r3ivWsM=onKJp94kRFx3hoARjBeFQ@mail.gmail.com>
Subject: JumbleQuery ma treat different GROUP BY expr as the same
To: PostgreSQL-development <pgsql-hackers@postgresql.org>
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Archived-At: <https://www.postgresql.org/message-id/CACJufxEy2W%2BtCqC7XuJ94r3ivWsM%3DonKJp94kRFx3hoARjBeFQ%40mail.gmail.com>
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hi.

drop table if exists t;
create table t(a text, b text, c int);
SELECT pg_stat_statements_reset() IS NOT NULL AS t;
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;

SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
 calls | rows |                                    query
-------+------+------------------------------------------------------------------------------
     0 |    0 | SELECT calls, rows, query FROM pg_stat_statements
ORDER BY query COLLATE "C"
     1 |    1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
     2 |    0 | explain(costs off, verbose) select count(*) from t group by a
     2 |    0 | explain(costs off, verbose) select count(*) from t group by a;
     1 |    0 | explain(costs off, verbose) select count(*) from t group by c
     1 |    0 | explain(costs off, verbose) select count(*) from t group by c;
(6 rows)

transformSelectStmt->transformGroupClause->transformGroupClauseExpr->addTargetToGroupList
will produce the same SortGroupClause node for "group by a" and "group by b".

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?


--
jian
https://www.enterprisedb.com/