Fix ORCA choosing wrong column type for CTAS with UNION ALL (#1431)

src/backend/optimizer/plan/orca.c

@@ -545,6 +545,10 @@ push_down_expr_mutator(Node *node, List *child_tlist)
 			{
 				((Const *) child_tle->expr)->consttypmod = ((Var *) node)->vartypmod;
 			}
+			else if (IsA(child_tle->expr, Var))
+			{
+				((Var *) child_tle->expr)->vartypmod = ((Var *) node)->vartypmod;
+			}
 
 			return (Node *) child_tle->expr;
 		}

src/test/regress/expected/union_gp.out

@@ -2342,6 +2342,36 @@ with result as (update r_1240 set a = a +1 where a < 5 returning *) select * fro
 drop table r_1240;
 drop table p1_1240;
 --
+-- Test CTAS with UNION ALL when branches have different typmods (issue #1431).
+-- ORCA should resolve the output column type to character varying (no length),
+-- same as the Postgres planner, instead of picking the first branch's typmod.
+--
+create table union_ctas_t1(id int, name varchar(1));
+create table union_ctas_t2(id int, name varchar(2));
+insert into union_ctas_t1 values (1, 'a');
+insert into union_ctas_t2 values (1, 'ab');
+create table union_ctas_result as
+  (select id, name from union_ctas_t1)
+  union all
+  (select id, name from union_ctas_t2);
+-- name column should be "character varying" without length, not varchar(1)
+select atttypmod from pg_attribute
+where attrelid = 'union_ctas_result'::regclass and attname = 'name';
+ atttypmod 
+-----------
+        -1
+(1 row)
+
+-- data should not be truncated
+select * from union_ctas_result order by name;
+ id | name 
+----+------
+  1 | a
+  1 | ab
+(2 rows)
+
+drop table union_ctas_t1, union_ctas_t2, union_ctas_result;
+--
 -- Clean up
 --
 DROP TABLE IF EXISTS T_a1 CASCADE;