From bf2d0462cd735f76bcf6eb8b399723674b2221ef Mon Sep 17 00:00:00 2001 From: Andrew Gierth Date: Tue, 28 Aug 2018 14:43:51 +0100 Subject: [PATCH] postgres_fdw: don't push ORDER BY with no vars (bug #15352) Commit aa09cd242 changed a condition in find_em_expr_for_rel from being a bms_equal comparison of relids to bms_is_subset, in order to support order by clauses on foreign joins. But this also allows through the degenerate case of expressions with no Vars at all (and hence empty relids), including integer constants which will be parsed unexpectedly on the remote (viz. "ERROR: ORDER BY position 0 is not in select list" as in the bug report). Repair by adding an additional !bms_is_empty test. Backpatch through to 9.6 where the aforementioned change was made. Per bug #15352 from Maksym Boguk; analysis and patch by me. Discussion: https://postgr.es/m/153518420278.1478.14875560810251994661@wrigleys.postgresql.org --- contrib/postgres_fdw/postgres_fdw.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index 0803c30a48..e4e330397e 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -5793,7 +5793,8 @@ find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel) { EquivalenceMember *em = lfirst(lc_em); - if (bms_is_subset(em->em_relids, rel->relids)) + if (bms_is_subset(em->em_relids, rel->relids) && + !bms_is_empty(em->em_relids)) { /* * If there is more than one equivalence member whose Vars are