cherry pick pingcap#15512 to release-2.1

Signed-off-by: sre-bot <sre-bot@pingcap.com>

executor/executor_test.go

@@ -3259,7 +3259,22 @@ func (s *testSuite3) TestIndexJoinTableDualPanic(c *C) {
 		Check(testkit.Rows("1 a"))
 }
 
+<<<<<<< HEAD
 func (s *testSuite3) TestUnionAutoSignedCast(c *C) {
+=======
+func (s *testSuite3) TestSortLeftJoinWithNullColumnInRightChildPanic(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1, t2")
+	tk.MustExec("create table t1(a int)")
+	tk.MustExec("create table t2(a int)")
+	tk.MustExec("insert into t1(a) select 1;")
+	tk.MustQuery("select b.n from t1 left join (select a as a, null as n from t2) b on b.a = t1.a order by t1.a").
+		Check(testkit.Rows("<nil>"))
+}
+
+func (s *testSuiteP1) TestUnionAutoSignedCast(c *C) {
+>>>>>>> 01db67b... chunk: make `mysql.TypeNull` be judged as fixedLen (#15512)
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")
 	tk.MustExec("drop table if exists t1,t2")

util/chunk/codec.go

@@ -171,7 +171,7 @@ func getFixedLen(colType *types.FieldType) int {
 	case mysql.TypeFloat:
 		return 4
 	case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong,
-		mysql.TypeLonglong, mysql.TypeDouble, mysql.TypeYear, mysql.TypeDuration:
+		mysql.TypeLonglong, mysql.TypeDouble, mysql.TypeYear, mysql.TypeDuration, mysql.TypeNull:
 		return 8
 	case mysql.TypeDate, mysql.TypeDatetime, mysql.TypeTimestamp:
 		return 16