Fix generation of EC join conditions at the wrong plan level.

get_baserel_parampathinfo previously assumed without checking that
the results of generate_join_implied_equalities "necessarily satisfy
join_clause_is_movable_into".  This turns out to be wrong in the
presence of outer joins, because the generated clauses could include
Vars that mustn't be evaluated below a relevant outer join.  That
led to applying clauses at the wrong plan level and possibly getting
incorrect query results.  We must check each clause's nullable_relids,
and really the right thing to do is test join_clause_is_movable_into.

However, trying to fix it that way exposes an oversight in
equivclass.c: it wasn't careful about marking join clauses for
appendrel children with the correct clause_relids.  That caused the
modified get_baserel_parampathinfo code to reject some clauses it
still needs to accept.  (See parallel commit for HEAD/v16 for more
commentary about that.)

Per bug #18429 from Benoît Ryder.  This misbehavior existed for
a long time before commit 2489d76c4, so patch v12-v15 this way.

Discussion: https://postgr.es/m/18429-8982d4a348cc86c6@postgresql.org

1 files changed, 15 insertions, 0 deletions

diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index e54da55924e..94387fdaca8 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -1465,6 +1465,21 @@ create_join_clause(PlannerInfo *root,
 												  rightem->em_nullable_relids),
 										ec->ec_min_security);
 
+	/*
+	 * If either EM is a child, force the clause's clause_relids to include
+	 * the relid(s) of the child rel.  In normal cases it would already, but
+	 * not if we are considering appendrel child relations with pseudoconstant
+	 * translated variables (i.e., UNION ALL sub-selects with constant output
+	 * items).  We must do this so that join_clause_is_movable_into() will
+	 * think that the clause should be evaluated at the correct place.
+	 */
+	if (leftem->em_is_child)
+		rinfo->clause_relids = bms_add_members(rinfo->clause_relids,
+											   leftem->em_relids);
+	if (rightem->em_is_child)
+		rinfo->clause_relids = bms_add_members(rinfo->clause_relids,
+											   rightem->em_relids);
+
 	/* Mark the clause as redundant, or not */
 	rinfo->parent_ec = parent_ec;