Re: JumbleQuery ma treat different GROUP BY expr as the same

jian he <jian(dot)universality(at)gmail(dot)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->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