partition_key_collation.diff

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 948afd90..bf96c0ce 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -7998,6 +7998,10 @@ create_partitionwise_grouping_paths(PlannerInfo *root,
  *
  * Returns true, if all the partition keys of the given relation are part of
  * the GROUP BY clauses, false otherwise.
+ * NB: partition key's collation is stored at part_scheme->partcollation.
+ * When comparing GROUP BY clauses with partition keys, we need check
+ * collation of part_scheme->partcollation, not the collation of input_rel->partexprs,
+ * since these two maybe different.
  */
 static bool
 group_by_has_partkey(RelOptInfo *input_rel,
@@ -8007,6 +8011,8 @@ group_by_has_partkey(RelOptInfo *input_rel,
 	List	   *groupexprs = get_sortgrouplist_exprs(groupClause, targetList);
 	int			cnt = 0;
 	int			partnatts;
+	Oid			groupcoll = InvalidOid;
+	Oid			partcoll = InvalidOid;
 
 	/* Input relation should be partitioned. */
 	Assert(input_rel->part_scheme);
@@ -8023,15 +8029,31 @@ group_by_has_partkey(RelOptInfo *input_rel,
 		ListCell   *lc;
 		bool		found = false;
 
+		partcoll	= input_rel->part_scheme->partcollation[cnt];
 		foreach(lc, partexprs)
 		{
+			ListCell   *lg;
 			Expr	   *partexpr = lfirst(lc);
 
-			if (list_member(groupexprs, partexpr))
+			foreach(lg, groupexprs)
 			{
-				found = true;
-				break;
+				Expr *groupexpr = lfirst(lg);
+				groupcoll = exprCollation((Node *) groupexpr);
+
+				if (partcoll == groupcoll)
+				{
+					if (IsA(groupexpr, RelabelType))
+						groupexpr = ((RelabelType *) groupexpr)->arg;
+
+					if (equal(groupexpr, partexpr))
+					{
+						found = true;
+						break;
+					}
+				}
 			}
+			if (found)
+				break;
 		}
 
 		/*