Re: Missing Group Key in grouped aggregate

=?UTF-8?Q?Erik_Nordstr=C3=B6m?= <erik@timescale.com> writes:
> I noticed that, beginning with PG16, grouped aggregates are missing the
> "Group Key" in the EXPLAIN output.

> It seems the Agg node has numCols (number of grouping cols) set to zero in
> queries like

> SELECT foo, count(*) FROM bar WHERE foo=1 GROUP BY foo;

> In PG15, the "Group Key" is shown and the Agg node has numCols set as
> expected.

Looks sane to me: the planner now notices that there can only
be one group so it doesn't tell the GroupAgg node to worry about
making groups.  If it were missing in a case where there could be
multiple output groups, yes that'd be a bug.

If you want to run it to ground you could bisect to see where the
behavior changed, but you'd probably just find it was intentional.

            regards, tom lane