On Thu, Mar 7, 2024 at 4:39 PM David Rowley <dgrowle...@gmail.com> wrote:
> On Thu, 7 Mar 2024 at 19:09, Michał Kłeczek <mic...@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. > > I wonder if we need a test... > Yes. -- Best Wishes, Ashutosh Bapat
