From 7f2c420da9e634755b6d78155cd0f21ba87de1e2 Mon Sep 17 00:00:00 2001
From: eaydingol <ebruaydin@gmail.com>
Date: Tue, 30 Jul 2024 08:50:53 +0000
Subject: [PATCH] Fix 7663 by checking if the limit is null when the limit is
 computed with respect to the offset.

---
 .../planner/multi_logical_optimizer.c         | 29 +++++++++-----
 .../regress/expected/multi_limit_clause.out   | 40 +++++++++++++++++++
 src/test/regress/sql/multi_limit_clause.sql   |  9 +++++
 3 files changed, 69 insertions(+), 9 deletions(-)

diff --git a/src/backend/distributed/planner/multi_logical_optimizer.c b/src/backend/distributed/planner/multi_logical_optimizer.c
index 76e38237a..eda8d399e 100644
--- a/src/backend/distributed/planner/multi_logical_optimizer.c
+++ b/src/backend/distributed/planner/multi_logical_optimizer.c
@@ -4753,22 +4753,33 @@ 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);
+		if (!workerLimitConst->constisnull)
+		{
+			/* Only update the worker limit if the const is not null.*/
+			Const *workerOffsetConst = (Const *) limitOffset;
+			int64 workerLimitCount = DatumGetInt64(workerLimitConst->constvalue);
+			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;
diff --git a/src/test/regress/expected/multi_limit_clause.out b/src/test/regress/expected/multi_limit_clause.out
index 65304b777..4f39a6d92 100644
--- a/src/test/regress/expected/multi_limit_clause.out
+++ b/src/test/regress/expected/multi_limit_clause.out
@@ -521,6 +521,46 @@ 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)
+
 SET client_min_messages TO NOTICE;
 -- non constants should not push down
 CREATE OR REPLACE FUNCTION my_limit()
diff --git a/src/test/regress/sql/multi_limit_clause.sql b/src/test/regress/sql/multi_limit_clause.sql
index 8d14bbbc8..94b1ae3f1 100644
--- a/src/test/regress/sql/multi_limit_clause.sql
+++ b/src/test/regress/sql/multi_limit_clause.sql
@@ -222,6 +222,15 @@ 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;
+
 SET client_min_messages TO NOTICE;
 
 -- non constants should not push down