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

On Sat, Jan 10, 2026 at 11:46:27AM -0500, Tom Lane wrote:
> 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.

The difference of behavior is between v17 and v18, as an effect of
247dea89f761. I know that we should not break query ID computations
in stable branches, but v18 is very recent and we still have many
years to support it.. So I would like to suggest that we make an
exception and backpatch a fix to v18. This behavior is not cool for
users.

This issue also points to a gap in the regression of
pg_stat_statements, where we have never bothered testing patterns of
GROUP BY with the same table and different attributes. Jian, would
you like to write a patch?
--
Michael