diff --git a/planner/core/physical_plan_test.go b/planner/core/physical_plan_test.go
index 458fe62fba065..3d1bce80e281d 100644
--- a/planner/core/physical_plan_test.go
+++ b/planner/core/physical_plan_test.go
@@ -198,6 +198,10 @@ func (s *testPlanSuite) TestDAGPlanBuilderSimpleCase(c *C) {
 			sql:  "select * from ((SELECT 1 a,6 b) UNION (SELECT 2,5) UNION (SELECT 2, 4) ORDER BY 1) t order by 1, 2",
 			best: "UnionAll{Dual->Projection->Dual->Projection->Dual->Projection}->HashAgg->Sort->Sort",
 		},
+		{
+			sql:  "select * from (select *, NULL as xxx from t) t order by xxx",
+			best: "TableReader(Table(t))->Projection",
+		},
 	}
 	for i, tt := range tests {
 		comment := Commentf("case:%v sql:%s", i, tt.sql)
diff --git a/planner/core/rule_column_pruning.go b/planner/core/rule_column_pruning.go
index 51e99cf7c71f7..508797b27958f 100644
--- a/planner/core/rule_column_pruning.go
+++ b/planner/core/rule_column_pruning.go
@@ -125,6 +125,8 @@ func (ls *LogicalSort) PruneColumns(parentUsedCols []*expression.Column) {
 				continue
 			}
 			ls.ByItems = append(ls.ByItems[:i], ls.ByItems[i+1:]...)
+		} else if ls.ByItems[i].Expr.GetType().Tp == mysql.TypeNull {
+			ls.ByItems = append(ls.ByItems[:i], ls.ByItems[i+1:]...)
 		} else {
 			parentUsedCols = append(parentUsedCols, cols...)
 		}