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Fix crash in postgres_fdw for provably-empty remote UPDATE/DELETE.

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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
This commit is contained in:
Tom Lane
2021-07-07 15:21:25 -04:00
parent e48f2afee6
commit 30a35bca3f
3 changed files with 27 additions and 1 deletions
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contrib/postgres_fdw/sql/postgres_fdw.sql
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@ -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