Fix NULL locus of Shared Scan.

src/backend/optimizer/plan/planshare.c

@@ -52,6 +52,9 @@ make_shareinputscan(PlannerInfo *root, Plan *inputplan)
 	sisc->scan.plan.plan_rows = inputplan->plan_rows;
 	sisc->scan.plan.plan_width = inputplan->plan_width;
 
+	sisc->scan.plan.locustype = inputplan->locustype;
+	sisc->scan.plan.parallel = 0; /* No parallel ShareInputScan */
+
 	return sisc;
 }
 

src/test/regress/expected/cbdb_parallel.out

@@ -3516,7 +3516,59 @@ WHERE e.salary > (
  David
 (2 rows)
 
-
+--
+-- Test https://github.com/apache/cloudberry/issues/1376
+--
+create table t1(a int, b int);
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'a' as the Apache Cloudberry data distribution key for this table.
+HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
+create table t2 (like t1);
+NOTICE:  table doesn't have 'DISTRIBUTED BY' clause, defaulting to distribution columns from LIKE table
+set gp_cte_sharing = on;
+explain(locus, costs off) with x as
+  (select a, count(*) as b from t1 group by a union all
+    select a, count(*) as b from t2 group by a)
+  select count(*) from x a join x b on a.a = b.b;
+                               QUERY PLAN                               
+------------------------------------------------------------------------
+ Finalize Aggregate
+   Locus: Entry
+   ->  Gather Motion 3:1  (slice1; segments: 3)
+         Locus: Entry
+         ->  Partial Aggregate
+               Locus: Hashed
+               ->  Hash Join
+                     Locus: Hashed
+                     Hash Cond: (b.b = a.a)
+                     ->  Redistribute Motion 3:3  (slice2; segments: 3)
+                           Locus: Hashed
+                           Hash Key: b.b
+                           ->  Subquery Scan on b
+                                 Locus: Strewn
+                                 ->  Shared Scan (share slice:id 2:0)
+                                       Locus: Hashed
+                     ->  Hash
+                           Locus: Hashed
+                           ->  Subquery Scan on a
+                                 Locus: Hashed
+                                 ->  Shared Scan (share slice:id 1:0)
+                                       Locus: Hashed
+                                       ->  Append
+                                             Locus: Hashed
+                                             ->  HashAggregate
+                                                   Locus: Hashed
+                                                   Group Key: t1.a
+                                                   ->  Seq Scan on t1
+                                                         Locus: Hashed
+                                             ->  HashAggregate
+                                                   Locus: Hashed
+                                                   Group Key: t2.a
+                                                   ->  Seq Scan on t2
+                                                         Locus: Hashed
+ Optimizer: Postgres query optimizer
+(35 rows)
+
+reset gp_cte_sharing;
 reset enable_parallel;
 reset min_parallel_table_scan_size;
 -- start_ignore

src/test/regress/sql/cbdb_parallel.sql

@@ -1132,7 +1132,20 @@ WHERE e.salary > (
     SELECT AVG(salary)
     FROM employees
     WHERE department_id = e.department_id);
-
+
+--
+-- Test https://github.com/apache/cloudberry/issues/1376
+--
+create table t1(a int, b int);
+create table t2 (like t1);
+set gp_cte_sharing = on;
+
+explain(locus, costs off) with x as
+  (select a, count(*) as b from t1 group by a union all
+    select a, count(*) as b from t2 group by a)
+  select count(*) from x a join x b on a.a = b.b;
+
+reset gp_cte_sharing;
 reset enable_parallel;
 reset min_parallel_table_scan_size;