Fix bug in cbc1279 to handle nested Append correctly

A non-leaf partition with a subplan that is an Append node was
omitted from PlannedStmt.unprunableRelids because it was mistakenly
included in PlannerGlobal.prunableRelids due to the way
PartitionedRelPruneInfo.leafpart_rti_map[] is constructed. This
happened when a non-leaf partition used an unflattened Append or
MergeAppend.  As a result, ExecGetRangeTableRelation() reported an
error when called from CreatePartitionPruneState() to process the
partition's own PartitionPruneInfo, since it was treated as prunable
when it should not have been.

Reported-by: Alexander Lakhin <exclusion@gmail.com> (via sqlsmith)
Diagnosed-by: Tender Wang <tndrwang@gmail.com>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/74839af6-aadc-4f60-ae77-ae65f94bf607@gmail.com

Author: amitlan

src/backend/executor/execPartition.c

@@ -2589,9 +2589,9 @@ ExecFindMatchingSubPlans(PartitionPruneState *prunestate,
  * find_matching_subplans_recurse
  *		Recursive worker function for ExecFindMatchingSubPlans
  *
- * Adds valid (non-prunable) subplan IDs to *validsubplans and the RT indexes
- * of their corresponding leaf partitions to *validsubplan_rtis if
- * it's non-NULL.
+ * Adds valid (non-prunable) subplan IDs to *validsubplans. If
+ * *validsubplan_rtis is non-NULL, it also adds the RT indexes of their
+ * corresponding partitions, but only if they are leaf partitions.
  */
 static void
 find_matching_subplans_recurse(PartitionPruningData *prunedata,
@@ -2628,7 +2628,12 @@ find_matching_subplans_recurse(PartitionPruningData *prunedata,
 		{
 			*validsubplans = bms_add_member(*validsubplans,
 											pprune->subplan_map[i]);
-			if (validsubplan_rtis)
+
+			/*
+			 * Only report leaf partitions. Non-leaf partitions may appear
+			 * here when they use an unflattened Append or MergeAppend.
+			 */
+			if (validsubplan_rtis && pprune->leafpart_rti_map[i])
 				*validsubplan_rtis = bms_add_member(*validsubplan_rtis,
 													pprune->leafpart_rti_map[i]);
 		}

src/backend/partitioning/partprune.c

@@ -687,7 +687,14 @@ make_partitionedrel_pruneinfo(PlannerInfo *root, RelOptInfo *parentrel,
 			if (subplanidx >= 0)
 			{
 				present_parts = bms_add_member(present_parts, i);
-				leafpart_rti_map[i] = (int) partrel->relid;
+
+				/*
+				 * Non-leaf partitions may appear here when they use an
+				 * unflattened Append or MergeAppend. These should not be
+				 * included in prunableRelids.
+				 */
+				if (partrel->nparts == -1)
+					leafpart_rti_map[i] = (int) partrel->relid;
 
 				/* Record finding this subplan  */
 				subplansfound = bms_add_member(subplansfound, subplanidx);

src/test/regress/expected/partition_prune.out

@@ -4590,5 +4590,53 @@ table part_abc_view;
  2 | c | t
 (1 row)
 
+-- A case with nested MergeAppend with its own PartitionPruneInfo.
+create index on part_abc (a);
+alter table part_abc add d int;
+create table part_abc_3 partition of part_abc for values in (3, 4) partition by range (d);
+create table part_abc_3_1 partition of part_abc_3 for values from (minvalue) to (1);
+create table part_abc_3_2 partition of part_abc_3 for values from (1) to (100);
+create table part_abc_3_3 partition of part_abc_3 for values from (100) to (maxvalue);
+explain (costs off)
+select min(a) over (partition by a order by a) from part_abc where a >= stable_one() + 1 and d <= stable_one()
+union all
+select min(a) over (partition by a order by a) from part_abc where a >= stable_one() + 1 and d >= stable_one();
+                                          QUERY PLAN                                          
+----------------------------------------------------------------------------------------------
+ Append
+   ->  Subquery Scan on "*SELECT* 1_1"
+         ->  WindowAgg
+               ->  Append
+                     Subplans Removed: 1
+                     ->  Index Scan using part_abc_2_a_idx on part_abc_2 part_abc_1
+                           Index Cond: (a >= (stable_one() + 1))
+                           Filter: (d <= stable_one())
+                     ->  Merge Append
+                           Sort Key: part_abc_3.a
+                           Subplans Removed: 1
+                           ->  Index Scan using part_abc_3_1_a_idx on part_abc_3_1 part_abc_3
+                                 Index Cond: (a >= (stable_one() + 1))
+                                 Filter: (d <= stable_one())
+                           ->  Index Scan using part_abc_3_2_a_idx on part_abc_3_2 part_abc_4
+                                 Index Cond: (a >= (stable_one() + 1))
+                                 Filter: (d <= stable_one())
+   ->  Subquery Scan on "*SELECT* 2"
+         ->  WindowAgg
+               ->  Append
+                     Subplans Removed: 1
+                     ->  Index Scan using part_abc_2_a_idx on part_abc_2 part_abc_6
+                           Index Cond: (a >= (stable_one() + 1))
+                           Filter: (d >= stable_one())
+                     ->  Merge Append
+                           Sort Key: a
+                           Subplans Removed: 1
+                           ->  Index Scan using part_abc_3_2_a_idx on part_abc_3_2 part_abc_8
+                                 Index Cond: (a >= (stable_one() + 1))
+                                 Filter: (d >= stable_one())
+                           ->  Index Scan using part_abc_3_3_a_idx on part_abc_3_3 part_abc_9
+                                 Index Cond: (a >= (stable_one() + 1))
+                                 Filter: (d >= stable_one())
+(33 rows)
+
 drop view part_abc_view;
 drop table part_abc;

src/test/regress/sql/partition_prune.sql

@@ -1397,5 +1397,17 @@ using (select stable_one() + 2 as pid) as q join part_abc_1 pt1 on (q.pid = pt1.
 when matched then delete returning pt.a;
 table part_abc_view;
 
+-- A case with nested MergeAppend with its own PartitionPruneInfo.
+create index on part_abc (a);
+alter table part_abc add d int;
+create table part_abc_3 partition of part_abc for values in (3, 4) partition by range (d);
+create table part_abc_3_1 partition of part_abc_3 for values from (minvalue) to (1);
+create table part_abc_3_2 partition of part_abc_3 for values from (1) to (100);
+create table part_abc_3_3 partition of part_abc_3 for values from (100) to (maxvalue);
+explain (costs off)
+select min(a) over (partition by a order by a) from part_abc where a >= stable_one() + 1 and d <= stable_one()
+union all
+select min(a) over (partition by a order by a) from part_abc where a >= stable_one() + 1 and d >= stable_one();
+
 drop view part_abc_view;
 drop table part_abc;