planner, executor: split the range for unsigned pk of partition table…

… when limit is used (pingcap#40313)

close pingcap#40309

executor/partition_table_test.go

@@ -637,6 +637,17 @@ func TestOrderByandLimit(t *testing.T) {
 	}
 }
 
+func TestOrderByOnUnsignedPk(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table tunsigned_hash(a bigint unsigned primary key) partition by hash(a) partitions 6")
+	tk.MustExec("insert into tunsigned_hash values(25), (9279808998424041135)")
+	tk.MustQuery("select min(a) from tunsigned_hash").Check(testkit.Rows("25"))
+	tk.MustQuery("select max(a) from tunsigned_hash").Check(testkit.Rows("9279808998424041135"))
+}
+
 func TestBatchGetandPointGetwithHashPartition(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 

planner/core/task.go

@@ -1075,7 +1075,6 @@ func (p *PhysicalTopN) pushTopNDownToDynamicPartition(copTsk *copTask) (task, bo
 		if !propMatched {
 			return nil, false
 		}
-
 		idxScan.Desc = isDesc
 		childProfile := copTsk.plan().statsInfo()
 		newCount := p.Offset + p.Count
@@ -1103,6 +1102,8 @@ func (p *PhysicalTopN) pushTopNDownToDynamicPartition(copTsk *copTask) (task, bo
 			}
 		}
 		tblScan.Desc = isDesc
+		// SplitRangesAcrossInt64Boundary needs the KeepOrder flag. See that func and the struct tableResultHandler for more details.
+		tblScan.KeepOrder = true
 		childProfile := copTsk.plan().statsInfo()
 		newCount := p.Offset + p.Count
 		stats := deriveLimitStats(childProfile, float64(newCount))