On Thu, 7 Mar 2024 at 19:09, Michał Kłeczek <michal@kleczek.org> wrote: > > The following query: > > SELECT * FROM ( > SELECT 2023 AS year, * FROM remote_table_1 > UNION ALL > SELECT 2022 AS year, * FROM remote_table_2 > ) > ORDER BY year DESC; > > yields the following remote query: > > SELECT [columns] FROM remote_table_1 ORDER BY 2023 DESC > > and subsequently fails remote execution. > > > Not really sure where the problem is - the planner or postgres_fdw. > I guess it is postgres_fdw not filtering out ordering keys.
Interesting. I've attached a self-contained recreator for the casual passerby.
I think the fix should go in appendOrderByClause(). It's at that point we look for the EquivalenceMember for the relation and can easily discover if the em_expr is a Const. I think we can safely just skip doing any ORDER BY <const> stuff and not worry about if the literal format of the const will appear as a reference to an ordinal column position in the ORDER BY clause.
deparseSortGroupClause() calls deparseConst() with showtype = 1. appendOrderByClause() may want to do something similar for consistency. Or remove it from deparseSortGroupClause() as well?
Something like the attached patch I think should work.