From 64eed263ac474433d17f05b23df3018a38e71fca 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 d8ae029faa9..5bc8bca45f8 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -5169,7 +5169,8 @@ 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