On Mon, Jul 1, 2024 at 3:17 PM Ashutosh Bapat <ashutosh.bapat....@gmail.com> wrote:
> Hi All, > While reviewing Richard's patch for grouping sets, I stumbled upon > following explain output > > explain (costs off) > select distinct on (a, b) a, b > from (values (1, 1), (2, 2)) as t (a, b) where a = b > group by grouping sets((a, b), (a)) > order by a, b; > QUERY PLAN > ---------------------------------------------------------------- > Unique > -> Sort > Sort Key: "*VALUES*".column1, "*VALUES*".column2 > -> HashAggregate > Hash Key: "*VALUES*".column1, "*VALUES*".column2 > Hash Key: "*VALUES*".column1 > -> Values Scan on "*VALUES*" > Filter: (column1 = column2) > (8 rows) > > There is no VALUES.column1 and VALUES.column2 in the query. The alias t.a > and t.b do not appear anywhere in the explain output. I think explain > output should look like > explain (costs off) > select distinct on (a, b) a, b > from (values (1, 1), (2, 2)) as t (a, b) where a = b > group by grouping sets((a, b), (a)) > order by a, b; > QUERY PLAN > ---------------------------------------------------------------- > Unique > -> Sort > Sort Key: t.a, t.b > -> HashAggregate > Hash Key: t.a, t.b > Hash Key: t.a > -> Values Scan on "*VALUES*" t > Filter: (a = b) > (8 rows) > > I didn't get time to figure out the reason behind this, nor the history. > But I thought I would report it nonetheless. > I have looked into the issue and found that when subqueries are pulled up, a modifiable copy of the subquery is created for modification in the pull_up_simple_subquery() function. During this process, flatten_join_alias_vars() is called to flatten any join alias variables in the subquery's target list. However at this point, we lose subquery's alias. If you/hackers agree with my findings, I can provide a working patch soon. > -- > Best Wishes, > Ashutosh Bapat >
