fix-partition-pruning-with-isnull.patch

diff --git a/src/backend/partitioning/partprune.c b/src/backend/partitioning/partprune.c
index 7179b22a05..0fbc2dba33 100644
--- a/src/backend/partitioning/partprune.c
+++ b/src/backend/partitioning/partprune.c
@@ -3383,10 +3383,21 @@ perform_pruning_base_step(PartitionPruneContext *context,
 			bool		isnull;
 			Oid			cmpfn;
 
+			/*
+			 * IS NULL clause is not added into array of ExprStates
+			 * and thus 'stateidx' based on 'keyno' cannot be used to get
+			 * ExprStates array element. Use the index based on 'nvalues'
+			 * in order to obtain proper datum from the array.
+			 */
+			int			exprstateidx =
+				PruneCxtStateIdx(context->partnatts, opstep->step.step_id,
+								 nvalues);
+
 			expr = lfirst(lc1);
 			stateidx = PruneCxtStateIdx(context->partnatts,
 										opstep->step.step_id, keyno);
-			partkey_datum_from_expr(context, expr, stateidx,
+
+			partkey_datum_from_expr(context, expr, exprstateidx,
 									&datum, &isnull);
 
 			/*
diff --git a/src/test/regress/expected/partition_prune.out b/src/test/regress/expected/partition_prune.out
index bb1223e2b1..a16e08a405 100644
--- a/src/test/regress/expected/partition_prune.out
+++ b/src/test/regress/expected/partition_prune.out
@@ -1921,6 +1921,18 @@ explain (costs off) select * from hp where (a = 1 and b = 'abcde') or (a = 2 and
          Filter: (((a = 1) AND (b = 'abcde'::text)) OR ((a = 2) AND (b = 'xxx'::text)) OR ((a IS NULL) AND (b IS NULL)))
 (7 rows)
 
+-- test partition pruning with prepared statement and IS NULL clause.
+prepare stmt AS select * from hp where a is null and b = $1;
+explain (costs off) execute stmt('xxx');
+                 QUERY PLAN                 
+--------------------------------------------
+ Append
+   Subplans Removed: 3
+   ->  Seq Scan on hp2 hp_1
+         Filter: ((a IS NULL) AND (b = $1))
+(4 rows)
+
+deallocate stmt;
 -- test pruning when not all the partitions exist
 drop table hp1;
 drop table hp3;
diff --git a/src/test/regress/sql/partition_prune.sql b/src/test/regress/sql/partition_prune.sql
index 83fed54b8c..9cafbdd538 100644
--- a/src/test/regress/sql/partition_prune.sql
+++ b/src/test/regress/sql/partition_prune.sql
@@ -374,6 +374,11 @@ explain (costs off) select * from hp where a = 2 and b = 'xxx';
 explain (costs off) select * from hp where a = 1 and b = 'abcde';
 explain (costs off) select * from hp where (a = 1 and b = 'abcde') or (a = 2 and b = 'xxx') or (a is null and b is null);
 
+-- test partition pruning with prepared statement and IS NULL clause.
+prepare stmt AS select * from hp where a is null and b = $1;
+explain (costs off) execute stmt('xxx');
+deallocate stmt;
+
 -- test pruning when not all the partitions exist
 drop table hp1;
 drop table hp3;