Enhance regression test for issue 7891 to verify planner's handling of local and reference tables

src/test/regress/expected/issue_7891.out

@@ -1,3 +1,6 @@
+-- This construct has been used as a regression test to ensure that the planner
+-- correctly distinguishes between "local" and "reference" tables, avoiding an erroneous 0-task plan.
+-- https://github.com/citusdata/citus/issues/7891
 CREATE SCHEMA issue_7891;
 SET search_path TO issue_7891;
 
@@ -62,61 +65,8 @@ SELECT 't2_ref data' AS label, * FROM t2_ref;
 -- Historically might produce a 0-task plan if the planner incorrectly fails to
 -- treat t4_pg/t2_ref as local/reference.
 --
---- EXPLAIN of update (problem scenario) ---
-EXPLAIN (VERBOSE, COSTS OFF)
-UPDATE t6_pg
-   SET vkey = 43
- WHERE EXISTS (
-   SELECT (SELECT c15 FROM t2_ref)
-   FROM t4_pg
-);
-                                                                                                                               QUERY PLAN
----------------------------------------------------------------------
- Custom Scan (Citus Adaptive)
-   Task Count: 1
-   Tasks Shown: All
-   ->  Task
-         Query: UPDATE issue_7891.t6_pg SET vkey = 43 WHERE (EXISTS (SELECT (SELECT t2_ref.c15 FROM (SELECT NULL::integer AS vkey, NULL::integer AS pkey, NULL::timestamp without time zone AS c15 WHERE false) t2_ref(vkey, pkey, c15)) AS c15 FROM issue_7891.t4_pg))
-         Node: host=localhost port=xxxxx dbname=regression
-         ->  Update on issue_7891.t6_pg
-               InitPlan 1
-                 ->  Seq Scan on issue_7891.t4_pg
-               ->  Result
-                     Output: 43, t6_pg.ctid
-                     One-Time Filter: (InitPlan 1).col1
-                     ->  Seq Scan on issue_7891.t6_pg
-                           Output: t6_pg.ctid
-(14 rows)
 
-
---- EXPLAIN reversing subquery usage ---
-EXPLAIN (VERBOSE, COSTS OFF)
-UPDATE t6_pg
-   SET vkey = 43
- WHERE EXISTS (
-   SELECT (SELECT c22 FROM t4_pg)
-   FROM t2_ref
-);
-                                                                            QUERY PLAN
----------------------------------------------------------------------
- Custom Scan (Citus Adaptive)
-   Task Count: 1
-   Tasks Shown: All
-   ->  Task
-         Query: UPDATE issue_7891.t6_pg SET vkey = 43 WHERE (EXISTS (SELECT (SELECT t4_pg.c22 FROM issue_7891.t4_pg) AS c22 FROM issue_7891.t2_ref_363177 t2_ref))
-         Node: host=localhost port=xxxxx dbname=regression
-         ->  Update on issue_7891.t6_pg
-               InitPlan 1
-                 ->  Seq Scan on issue_7891.t2_ref_363177 t2_ref
-               ->  Result
-                     Output: 43, t6_pg.ctid
-                     One-Time Filter: (InitPlan 1).col1
-                     ->  Seq Scan on issue_7891.t6_pg
-                           Output: t6_pg.ctid
-(14 rows)
-
-
--- Now actually do the update to confirm it works
+-- The outer subquery iterates over every row in table t4_pg.
 UPDATE t6_pg
    SET vkey = 43
  WHERE EXISTS (
@@ -132,9 +82,23 @@ SELECT 't6_pg after' AS label, * FROM t6_pg;
 (1 row)
 
 
+-- The outer subquery iterates over rows from the reference table t2_ref
+UPDATE t6_pg 
+   SET vkey = 43
+ WHERE EXISTS ( 
+   SELECT (SELECT c22 FROM t4_pg) 
+   FROM t2_ref
+);
+ERROR:  relation "issue_7891.t6_pg" does not exist
+CONTEXT:  while executing command on localhost:xxxxx
+
+-- Show final data
+SELECT 't6_pg after' AS label, * FROM t6_pg;
+    label    | vkey | pkey  | c26
+---------------------------------------------------------------------
+ t6_pg after |   43 | 12000 |
+(1 row)
+
+
+SET client_min_messages TO WARNING;
 DROP SCHEMA issue_7891 CASCADE;
-NOTICE:  drop cascades to 4 other objects
-DETAIL:  drop cascades to table t2_ref
-drop cascades to table t4_pg
-drop cascades to table t6_pg
-drop cascades to table t2_ref_363177

src/test/regress/sql/issue_7891.sql

@@ -1,3 +1,6 @@
+-- This construct has been used as a regression test to ensure that the planner
+-- correctly distinguishes between "local" and "reference" tables, avoiding an erroneous 0-task plan.
+-- https://github.com/citusdata/citus/issues/7891
 CREATE SCHEMA issue_7891;
 SET search_path TO issue_7891;
 
@@ -42,25 +45,8 @@ SELECT 't2_ref data' AS label, * FROM t2_ref;
 -- Historically might produce a 0-task plan if the planner incorrectly fails to
 -- treat t4_pg/t2_ref as local/reference.
 --
---- EXPLAIN of update (problem scenario) ---
-EXPLAIN (VERBOSE, COSTS OFF)
-UPDATE t6_pg
-   SET vkey = 43
- WHERE EXISTS (
-   SELECT (SELECT c15 FROM t2_ref)
-   FROM t4_pg
-);
 
---- EXPLAIN reversing subquery usage ---
-EXPLAIN (VERBOSE, COSTS OFF)
-UPDATE t6_pg
-   SET vkey = 43
- WHERE EXISTS (
-   SELECT (SELECT c22 FROM t4_pg)
-   FROM t2_ref
-);
-
--- Now actually do the update to confirm it works
+-- The outer subquery iterates over every row in table t4_pg.
 UPDATE t6_pg
    SET vkey = 43
  WHERE EXISTS (
@@ -71,4 +57,16 @@ UPDATE t6_pg
 -- Show final data
 SELECT 't6_pg after' AS label, * FROM t6_pg;
 
+-- The outer subquery iterates over rows from the reference table t2_ref
+UPDATE t6_pg 
+   SET vkey = 43
+ WHERE EXISTS ( 
+   SELECT (SELECT c22 FROM t4_pg) 
+   FROM t2_ref
+);
+
+-- Show final data
+SELECT 't6_pg after' AS label, * FROM t6_pg;
+
+SET client_min_messages TO WARNING;
 DROP SCHEMA issue_7891 CASCADE;