From d40e3291c5c82717c6dd6d58735b8499fd080920 Mon Sep 17 00:00:00 2001
From: Henson Choi <assam258@gmail.com>
Date: Fri, 2 Oct 2026 23:53:56 +0900
Subject: [PATCH v1 1/2] Add tests for OLD/NEW aliases EXPLAIN prints in
 RETURNING SubPlans

EXPLAIN VERBOSE prints a reference to the OLD or NEW of a
ModifyTable in a SubPlan of its RETURNING list with the aliases of a
data-modifying CTE that was printed before it.

The expected output shows the behavior before the fix.  The next
commit fixes it and updates the output.
---
 src/test/regress/expected/returning.out | 64 +++++++++++++++++++++++++
 src/test/regress/sql/returning.sql      | 21 ++++++++
 2 files changed, 85 insertions(+)

diff --git a/src/test/regress/expected/returning.out b/src/test/regress/expected/returning.out
index 44d4438fb86..24db5074e45 100644
--- a/src/test/regress/expected/returning.out
+++ b/src/test/regress/expected/returning.out
@@ -1053,3 +1053,67 @@ MERGE INTO ret_nn USING (VALUES (2), (3)) AS src(a) ON ret_nn.a = src.a
 (2 rows)
 
 DROP TABLE ret_nn;
+-- EXPLAIN must print the OLD/NEW aliases of the ModifyTable that owns a
+-- RETURNING list also inside its SubPlans, even when a data-modifying CTE
+-- has set different aliases
+CREATE TABLE returning_e1 (k int, c int);
+CREATE TABLE returning_e2 (k int, c int);
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH x AS (UPDATE returning_e2 SET c = c + 1
+           RETURNING WITH (OLD AS o, NEW AS n) o.k)
+UPDATE returning_e1 SET c = c + 1
+  RETURNING WITH (OLD AS p, NEW AS q) p.c,
+    (SELECT count(*) FROM returning_e2 WHERE returning_e2.c = p.c) AS m,
+    (SELECT count(*) FROM returning_e2 WHERE returning_e2.c = q.c) AS m2;
+                           QUERY PLAN                            
+-----------------------------------------------------------------
+ Update on public.returning_e1
+   Output: p.c, (SubPlan expr_1), (SubPlan expr_2)
+   CTE x
+     ->  Update on public.returning_e2
+           Output: o.k
+           ->  Seq Scan on public.returning_e2
+                 Output: (returning_e2.c + 1), returning_e2.ctid
+   ->  Seq Scan on public.returning_e1
+         Output: (returning_e1.c + 1), returning_e1.ctid
+   SubPlan expr_1
+     ->  Aggregate
+           Output: count(*)
+           ->  Seq Scan on public.returning_e2 returning_e2_1
+                 Output: returning_e2_1.k, returning_e2_1.c
+                 Filter: (returning_e2_1.c = o.c)
+   SubPlan expr_2
+     ->  Aggregate
+           Output: count(*)
+           ->  Seq Scan on public.returning_e2 returning_e2_2
+                 Output: returning_e2_2.k, returning_e2_2.c
+                 Filter: (returning_e2_2.c = n.c)
+(21 rows)
+
+-- likewise when a SubPlan compares values returned by the CTE
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH x AS (UPDATE returning_e2 SET c = c + 1
+           RETURNING WITH (OLD AS o, NEW AS n) n.k, o.c AS oc)
+UPDATE returning_e1 SET c = c + 1
+  RETURNING WITH (OLD AS p) p.c,
+    (SELECT count(*) FROM x WHERE x.oc = p.c) AS m;
+                           QUERY PLAN                            
+-----------------------------------------------------------------
+ Update on public.returning_e1
+   Output: p.c, (SubPlan expr_1)
+   CTE x
+     ->  Update on public.returning_e2
+           Output: n.k, o.c
+           ->  Seq Scan on public.returning_e2
+                 Output: (returning_e2.c + 1), returning_e2.ctid
+   ->  Seq Scan on public.returning_e1
+         Output: (returning_e1.c + 1), returning_e1.ctid
+   SubPlan expr_1
+     ->  Aggregate
+           Output: count(*)
+           ->  CTE Scan on x
+                 Output: x.k, x.oc
+                 Filter: (x.oc = o.c)
+(15 rows)
+
+DROP TABLE returning_e1, returning_e2;
diff --git a/src/test/regress/sql/returning.sql b/src/test/regress/sql/returning.sql
index a893f47e34d..a6a4865a025 100644
--- a/src/test/regress/sql/returning.sql
+++ b/src/test/regress/sql/returning.sql
@@ -444,3 +444,24 @@ MERGE INTO ret_nn USING (VALUES (2), (3)) AS src(a) ON ret_nn.a = src.a
   RETURNING merge_action(), old.a IS NULL, new.a IS NULL;
 
 DROP TABLE ret_nn;
+
+-- EXPLAIN must print the OLD/NEW aliases of the ModifyTable that owns a
+-- RETURNING list also inside its SubPlans, even when a data-modifying CTE
+-- has set different aliases
+CREATE TABLE returning_e1 (k int, c int);
+CREATE TABLE returning_e2 (k int, c int);
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH x AS (UPDATE returning_e2 SET c = c + 1
+           RETURNING WITH (OLD AS o, NEW AS n) o.k)
+UPDATE returning_e1 SET c = c + 1
+  RETURNING WITH (OLD AS p, NEW AS q) p.c,
+    (SELECT count(*) FROM returning_e2 WHERE returning_e2.c = p.c) AS m,
+    (SELECT count(*) FROM returning_e2 WHERE returning_e2.c = q.c) AS m2;
+-- likewise when a SubPlan compares values returned by the CTE
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH x AS (UPDATE returning_e2 SET c = c + 1
+           RETURNING WITH (OLD AS o, NEW AS n) n.k, o.c AS oc)
+UPDATE returning_e1 SET c = c + 1
+  RETURNING WITH (OLD AS p) p.c,
+    (SELECT count(*) FROM x WHERE x.oc = p.c) AS m;
+DROP TABLE returning_e1, returning_e2;
-- 
2.54.0 (Apple Git-157)