1 files changed, 27 insertions, 5 deletions

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index ae51c0e0b0c..5f6d2bad7be 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -83,7 +83,8 @@ static Plan *create_gating_plan(PlannerInfo *root, Path *path, Plan *plan,
 				   List *gating_quals);
 static Plan *create_join_plan(PlannerInfo *root, JoinPath *best_path);
 static Plan *create_append_plan(PlannerInfo *root, AppendPath *best_path);
-static Plan *create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path);
+static Plan *create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
+						 int flags);
 static Result *create_result_plan(PlannerInfo *root, ResultPath *best_path);
 static ProjectSet *create_project_set_plan(PlannerInfo *root, ProjectSetPath *best_path);
 static Material *create_material_plan(PlannerInfo *root, MaterialPath *best_path,
@@ -391,7 +392,8 @@ create_plan_recurse(PlannerInfo *root, Path *best_path, int flags)
 			break;
 		case T_MergeAppend:
 			plan = create_merge_append_plan(root,
-											(MergeAppendPath *) best_path);
+											(MergeAppendPath *) best_path,
+											flags);
 			break;
 		case T_Result:
 			if (IsA(best_path, ProjectionPath))
@@ -1130,11 +1132,14 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path)
  *	  Returns a Plan node.
  */
 static Plan *
-create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
+create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
+						 int flags)
 {
 	MergeAppend *node = makeNode(MergeAppend);
 	Plan	   *plan = &node->plan;
 	List	   *tlist = build_path_tlist(root, &best_path->path);
+	int			orig_tlist_length = list_length(tlist);
+	bool		tlist_was_changed;
 	List	   *pathkeys = best_path->path.pathkeys;
 	List	   *subplans = NIL;
 	ListCell   *subpaths;
@@ -1151,7 +1156,12 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
 	plan->lefttree = NULL;
 	plan->righttree = NULL;
 
-	/* Compute sort column info, and adjust MergeAppend's tlist as needed */
+	/*
+	 * Compute sort column info, and adjust MergeAppend's tlist as needed.
+	 * Because we pass adjust_tlist_in_place = true, we may ignore the
+	 * function result; it must be the same plan node.  However, we then need
+	 * to detect whether any tlist entries were added.
+	 */
 	(void) prepare_sort_from_pathkeys(plan, pathkeys,
 									  best_path->path.parent->relids,
 									  NULL,
@@ -1161,6 +1171,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
 									  &node->sortOperators,
 									  &node->collations,
 									  &node->nullsFirst);
+	tlist_was_changed = (orig_tlist_length != list_length(plan->targetlist));
 
 	/*
 	 * Now prepare the child plans.  We must apply prepare_sort_from_pathkeys
@@ -1227,7 +1238,18 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
 		flatten_partitioned_rels(best_path->partitioned_rels);
 	node->mergeplans = subplans;
 
-	return (Plan *) node;
+	/*
+	 * If prepare_sort_from_pathkeys added sort columns, but we were told to
+	 * produce either the exact tlist or a narrow tlist, we should get rid of
+	 * the sort columns again.  We must inject a projection node to do so.
+	 */
+	if (tlist_was_changed && (flags & (CP_EXACT_TLIST | CP_SMALL_TLIST)))
+	{
+		tlist = list_truncate(list_copy(plan->targetlist), orig_tlist_length);
+		return inject_projection_plan(plan, tlist, plan->parallel_safe);
+	}
+	else
+		return plan;
 }
 
 /*