step2.txt

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diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index 1095b73dac..b612420547 100644
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -432,6 +432,21 @@ group_keys_reorder_by_pathkeys(List *pathkeys, List **group_pathkeys,
 	return n;
 }
 
+static bool
+duplicated_pathkey_combination(List *infos, List *pathkeys)
+{
+	ListCell *lc;
+
+	foreach (lc, infos)
+	{
+		PathKeyInfo *info = lfirst_node(PathKeyInfo, lc);
+
+		if (compare_pathkeys(pathkeys, info->pathkeys) == PATHKEYS_EQUAL)
+			return true;
+	}
+	return false;
+}
+
 /*
  * get_useful_group_keys_orderings
  *		Determine which orderings of GROUP BY keys are potentially interesting.
@@ -491,7 +506,7 @@ get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
 
 		if (n > 0 &&
 			(enable_incremental_sort || n == root->num_groupby_pathkeys) &&
-			compare_pathkeys(pathkeys, root->group_pathkeys) != PATHKEYS_EQUAL)
+			!duplicated_pathkey_combination(infos, pathkeys))
 		{
 			info = makeNode(PathKeyInfo);
 			info->pathkeys = pathkeys;
@@ -514,8 +529,9 @@ get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
 										   &clauses,
 										   root->num_groupby_pathkeys);
 
-		if (n > 0 && compare_pathkeys(pathkeys, root->group_pathkeys) != PATHKEYS_EQUAL &&
-			(enable_incremental_sort || n == list_length(root->sort_pathkeys)))
+		if (n > 0 &&
+			(enable_incremental_sort || n == list_length(root->sort_pathkeys)) &&
+			!duplicated_pathkey_combination(infos, pathkeys))
 		{
 			info = makeNode(PathKeyInfo);
 			info->pathkeys = pathkeys;