Check if the limit is null

src/backend/distributed/planner/multi_logical_optimizer.c

@@ -4753,22 +4753,35 @@ WorkerLimitCount(Node *limitCount, Node *limitOffset, OrderByLimitReference
 	if (workerLimitNode != NULL && limitOffset != NULL)
 	{
 		Const *workerLimitConst = (Const *) workerLimitNode;
-		Const *workerOffsetConst = (Const *) limitOffset;
-		int64 workerLimitCount = DatumGetInt64(workerLimitConst->constvalue);
-		int64 workerOffsetCount = DatumGetInt64(workerOffsetConst->constvalue);
 
-		workerLimitCount = workerLimitCount + workerOffsetCount;
-		workerLimitNode = (Node *) MakeIntegerConstInt64(workerLimitCount);
+		/* Only update the worker limit if the const is not null.*/
+		if (!workerLimitConst->constisnull)
+		{
+			Const *workerOffsetConst = (Const *) limitOffset;
+			int64 workerLimitCount = DatumGetInt64(workerLimitConst->constvalue);
+
+			/* If the offset is null, it defaults to 0 when cast to int64. */
+			int64 workerOffsetCount = DatumGetInt64(workerOffsetConst->constvalue);
+			workerLimitCount = workerLimitCount + workerOffsetCount;
+			workerLimitNode = (Node *) MakeIntegerConstInt64(workerLimitCount);
+		}
 	}
 
 	/* display debug message on limit push down */
 	if (workerLimitNode != NULL)
 	{
 		Const *workerLimitConst = (Const *) workerLimitNode;
-		int64 workerLimitCount = DatumGetInt64(workerLimitConst->constvalue);
+		if (!workerLimitConst->constisnull)
+		{
+			int64 workerLimitCount = DatumGetInt64(workerLimitConst->constvalue);
 
-		ereport(DEBUG1, (errmsg("push down of limit count: " INT64_FORMAT,
-								workerLimitCount)));
+			ereport(DEBUG1, (errmsg("push down of limit count: " INT64_FORMAT,
+									workerLimitCount)));
+		}
+		else
+		{
+			ereport(DEBUG1, (errmsg("push down of limit count: ALL")));
+		}
 	}
 
 	return workerLimitNode;

src/test/regress/expected/multi_limit_clause.out

@@ -521,6 +521,86 @@ SELECT
           1 |    1
 (1 row)
 
+-- check if we can correctly push the limit when it is null
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey LIMIT null;
+DEBUG:  push down of limit count: ALL
+ l_orderkey
+---------------------------------------------------------------------
+          1
+          1
+          1
+          1
+          1
+          1
+          2
+(7 rows)
+
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey OFFSET 1 LIMIT null;
+DEBUG:  push down of limit count: ALL
+ l_orderkey
+---------------------------------------------------------------------
+          1
+          1
+          1
+          1
+          1
+          2
+(6 rows)
+
+SELECT count(*) FROM lineitem LIMIT null;
+DEBUG:  push down of limit count: ALL
+ count
+---------------------------------------------------------------------
+ 12000
+(1 row)
+
+SELECT count(*) FROM lineitem OFFSET 0 LIMIT null;
+DEBUG:  push down of limit count: ALL
+ count
+---------------------------------------------------------------------
+ 12000
+(1 row)
+
+-- check if we push the right limit when both offset and limit are given
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey OFFSET 1 LIMIT 3;
+DEBUG:  push down of limit count: 4
+ l_orderkey
+---------------------------------------------------------------------
+          1
+          1
+          1
+(3 rows)
+
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey OFFSET null LIMIT 1;
+DEBUG:  push down of limit count: 1
+ l_orderkey
+---------------------------------------------------------------------
+          1
+(1 row)
+
+-- check if we can correctly push the limit when it is all
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 2 LIMIT all;
+DEBUG:  push down of limit count: ALL
+ l_orderkey
+---------------------------------------------------------------------
+          1
+          1
+          1
+          1
+          1
+          1
+(6 rows)
+
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 2 OFFSET 2 LIMIT all;
+DEBUG:  push down of limit count: ALL
+ l_orderkey
+---------------------------------------------------------------------
+          1
+          1
+          1
+          1
+(4 rows)
+
 SET client_min_messages TO NOTICE;
 -- non constants should not push down
 CREATE OR REPLACE FUNCTION my_limit()

src/test/regress/sql/multi_limit_clause.sql

@@ -222,6 +222,25 @@ SELECT
 	ORDER BY 2 DESC, 1
 	LIMIT 5;
 
+-- check if we can correctly push the limit when it is null
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey LIMIT null;
+
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey OFFSET 1 LIMIT null;
+
+SELECT count(*) FROM lineitem LIMIT null;
+
+SELECT count(*) FROM lineitem OFFSET 0 LIMIT null;
+
+-- check if we push the right limit when both offset and limit are given
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey OFFSET 1 LIMIT 3;
+
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 3 ORDER BY l_orderkey OFFSET null LIMIT 1;
+
+-- check if we can correctly push the limit when it is all
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 2 LIMIT all;
+
+SELECT l_orderkey FROM lineitem WHERE l_orderkey < 2 OFFSET 2 LIMIT all;
+
 SET client_min_messages TO NOTICE;
 
 -- non constants should not push down