From 103e8e9fd2c7ab5a006d6a2ccd9eb4e0274a5c15 Mon Sep 17 00:00:00 2001
From: William Bernbaum <wbernbaum@dwdev.com>
Date: Wed, 26 Aug 2026 08:53:01 -0700
Subject: [PATCH v1 05/16] Take a pushed-down deduplication as the DISTINCT
 result

Additionally, clear the 'Partial' label when it no longer applies to a grouping.
---
 src/backend/optimizer/plan/planner.c | 48 ++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index a605387dcaa..750b430f495 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -4031,6 +4031,31 @@ get_number_of_groups(PlannerInfo *root,
 	return dNumGroups;
 }
 
+/*
+ * complete_dedup_path
+ *	  Clear the partial mark on a pushed-down deduplication.
+ *
+ * A deduplication is pushed down marked partial, which EXPLAIN would misreport
+ * once the path is taken as the finished grouping.  Only the label changes.
+ */
+static Path *
+complete_dedup_path(Path *path)
+{
+	AggPath    *aggpath;
+
+	if (!IsA(path, AggPath))
+		return path;
+
+	if (((AggPath *) path)->aggsplit != AGGSPLIT_INITIAL_SERIAL)
+		return path;
+
+	aggpath = makeNode(AggPath);
+	memcpy(aggpath, path, sizeof(AggPath));
+	aggpath->aggsplit = AGGSPLIT_SIMPLE;
+
+	return (Path *) aggpath;
+}
+
 /*
  * create_grouping_paths
  *
@@ -5083,6 +5108,29 @@ create_distinct_paths(PlannerInfo *root, RelOptInfo *input_rel,
 	/* now build distinct paths based on input_rel's partial_pathlist */
 	create_partial_distinct_paths(root, input_rel, distinct_rel, target);
 
+	/*
+	 * A pushed-down deduplication already groups by the DISTINCT expressions,
+	 * so its rows are the result.  Neither Sort nor Unique projects, so add a
+	 * projection onto the target.
+	 */
+	if (root->agg_clause_list == NIL &&
+		input_rel->grouped_rel != NULL &&
+		!IS_DUMMY_REL(input_rel->grouped_rel) &&
+		input_rel->grouped_rel->pathlist != NIL)
+	{
+		ListCell   *lc;
+
+		foreach(lc, input_rel->grouped_rel->pathlist)
+		{
+			Path	   *path = (Path *) lfirst(lc);
+
+			add_path(distinct_rel,
+					 (Path *) create_projection_path(root, distinct_rel,
+													 complete_dedup_path(path),
+													 target));
+		}
+	}
+
 	/* Give a helpful error if we failed to create any paths */
 	if (distinct_rel->pathlist == NIL)
 		ereport(ERROR,