ddl: Fix default value of a newly added enum column (#20798) (#20999)

ddl/column.go

@@ -602,10 +602,21 @@ func generateOriginDefaultValue(col *model.ColumnInfo) (interface{}, error) {
 	var err error
 	odValue := col.GetDefaultValue()
 	if odValue == nil && mysql.HasNotNullFlag(col.Flag) {
-		zeroVal := table.GetZeroValue(col)
-		odValue, err = zeroVal.ToString()
-		if err != nil {
-			return nil, errors.Trace(err)
+		switch col.Tp {
+		// Just use enum field's first element for OriginDefaultValue.
+		case mysql.TypeEnum:
+			defEnum, verr := types.ParseEnumValue(col.FieldType.Elems, 1)
+			if verr != nil {
+				return nil, errors.Trace(verr)
+			}
+			defVal := types.NewMysqlEnumDatum(defEnum)
+			return defVal.ToString()
+		default:
+			zeroVal := table.GetZeroValue(col)
+			odValue, err = zeroVal.ToString()
+			if err != nil {
+				return nil, errors.Trace(err)
+			}
 		}
 	}
 

ddl/db_integration_test.go

@@ -2059,3 +2059,32 @@ func (s *testIntegrationSuite3) TestIssue20490(c *C) {
 
 	tk.MustQuery("select b from issue20490 order by a;").Check(testkit.Rows("1", "1", "<nil>"))
 }
+
+func (s *testIntegrationSuite3) TestIssue20741WithEnumField(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists issue20741")
+	tk.MustExec("create table issue20741(id int primary key, c int)")
+	tk.MustExec("insert into issue20741(id, c) values(1, 2), (2, 2)")
+	tk.MustExec("alter table issue20741 add column cc enum('a', 'b', 'c', 'd') not null")
+	tk.MustExec("update issue20741 set c=2 where id=1")
+	tk.MustQuery("select * from issue20741").Check(testkit.Rows("1 2 a", "2 2 a"))
+	tk.MustQuery("select * from issue20741 where cc = 0").Check(testkit.Rows())
+	tk.MustQuery("select * from issue20741 where cc = 1").Check(testkit.Rows("1 2 a", "2 2 a"))
+}
+
+func (s *testIntegrationSuite3) TestIssue20741WithSetField(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists issue20741_2")
+	tk.MustExec("create table issue20741_2(id int primary key, c int)")
+	tk.MustExec("insert into issue20741_2(id, c) values(1, 2), (2, 2)")
+	tk.MustExec("alter table issue20741_2 add column cc set('a', 'b', 'c', 'd') not null")
+	tk.MustExec("update issue20741_2 set c=2 where id=1")
+	tk.MustQuery("select * from issue20741_2").Check(testkit.Rows("1 2 ", "2 2 "))
+	tk.MustQuery("select * from issue20741_2 where cc = 0").Check(testkit.Rows("1 2 ", "2 2 "))
+	tk.MustQuery("select * from issue20741_2 where cc = 1").Check(testkit.Rows())
+	_, err := tk.Exec("insert into issue20741_2(id, c) values (3, 3)")
+	c.Assert(err, NotNil)
+	c.Assert(err.Error(), Equals, "[table:1364]Field 'cc' doesn't have a default value")
+}