From 30a35bca3f9306f87ca8db095ddac2ba62156934 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 7 Jul 2021 15:21:25 -0400
Subject: Fix crash in postgres_fdw for provably-empty remote UPDATE/DELETE.

In 86dc90056, I'd written find_modifytable_subplan with the assumption
that if the immediate child of a ModifyTable is a Result, it must be
a projecting Result with a subplan.  However, if the UPDATE or DELETE
has a provably-constant-false WHERE clause, that's not so: we'll
generate a dummy subplan with a childless Result.  Add the missing
null-check so we don't crash on such cases.

Per report from Alexander Pyhalov.

Discussion: https://postgr.es/m/b9a6f53549456b2f3e2fd150dcd79d72@postgrespro.ru
---
 contrib/postgres_fdw/sql/postgres_fdw.sql | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'contrib/postgres_fdw/sql/postgres_fdw.sql')

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 911f171d812..c283e747154 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1738,6 +1738,10 @@ DROP TRIGGER trig_local_before ON loc1;
 
 
 -- Test direct foreign table modification functionality
+EXPLAIN (verbose, costs off)
+DELETE FROM rem1;                 -- can be pushed down
+EXPLAIN (verbose, costs off)
+DELETE FROM rem1 WHERE false;     -- currently can't be pushed down
 
 -- Test with statement-level triggers
 CREATE TRIGGER trig_stmt_before
-- 
cgit v1.2.3

