From 1771d675709984eaa6838ec6e6c8ac424001d0ce Mon Sep 17 00:00:00 2001
From: yj <mail2fish@gmail.com>
Date: Thu, 27 Sep 2018 18:02:05 +0800
Subject: [PATCH] ddl: allow enum to append values (#7767)

---
 ddl/db_change_test.go | 50 +++++++++++++++++++++++++++++++++++++++++++
 ddl/ddl_api.go        | 17 ++++++++++++++-
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/ddl/db_change_test.go b/ddl/db_change_test.go
index 33eb71eee0bf0..b8550c4bcdd83 100644
--- a/ddl/db_change_test.go
+++ b/ddl/db_change_test.go
@@ -349,6 +349,56 @@ type expectQuery struct {
 	rows []string
 }
 
+func (s *testStateChangeSuite) TestAppendEnum(c *C) {
+	_, err := s.se.Execute(context.Background(), `create table t (
+			c1 varchar(64),
+			c2 enum('N','Y') not null default 'N',
+			c3 timestamp on update current_timestamp,
+			c4 int primary key,
+			unique key idx2 (c2, c3))`)
+	c.Assert(err, IsNil)
+	defer s.se.Execute(context.Background(), "drop table t")
+	_, err = s.se.Execute(context.Background(), "insert into t values('a', 'N', '2017-07-01', 8)")
+	c.Assert(err, IsNil)
+	// Make sure these sqls use the the plan of index scan.
+	_, err = s.se.Execute(context.Background(), "drop stats t")
+	c.Assert(err, IsNil)
+	se, err := session.CreateSession(s.store)
+	c.Assert(err, IsNil)
+	_, err = se.Execute(context.Background(), "use test_db_state")
+	c.Assert(err, IsNil)
+
+	_, err = s.se.Execute(context.Background(), "insert into t values('a', 'A', '2018-09-19', 9)")
+	c.Assert(err.Error(), Equals, "[table:1366]Incorrect enum value: 'A' for column 'c2' at row 1")
+	failAlterTableSQL1 := "alter table t change c2 c2 enum('N') DEFAULT 'N'"
+	_, err = s.se.Execute(context.Background(), failAlterTableSQL1)
+	c.Assert(err.Error(), Equals, "[ddl:203]unsupported modify column the number of enum column's elements is less than the original: 2")
+	failAlterTableSQL2 := "alter table t change c2 c2 int default 0"
+	_, err = s.se.Execute(context.Background(), failAlterTableSQL2)
+	c.Assert(err.Error(), Equals, "[ddl:203]unsupported modify column charset binary not match origin utf8")
+	alterTableSQL := "alter table t change c2 c2 enum('N','Y','A') DEFAULT 'A'"
+	_, err = s.se.Execute(context.Background(), alterTableSQL)
+	c.Assert(err, IsNil)
+	_, err = se.Execute(context.Background(), "insert into t values('a', 'A', '2018-09-20', 10)")
+	c.Assert(err, IsNil)
+	_, err = se.Execute(context.Background(), "insert into t (c1, c3, c4) values('a', '2018-09-21', 11)")
+	c.Assert(err, IsNil)
+
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test_db_state")
+	result, err := s.execQuery(tk, "select c4, c2 from t order by c4 asc")
+	c.Assert(err, IsNil)
+	expected := []string{"8 N", "10 A", "11 A"}
+	checkResult(result, testkit.Rows(expected...))
+
+	_, err = s.se.Execute(context.Background(), "update t set c2='N' where c4 = 10")
+	c.Assert(err, IsNil)
+	result, err = s.execQuery(tk, "select c2 from t where c4 = 10")
+	c.Assert(err, IsNil)
+	expected = []string{"8 N", "10 N", "11 A"}
+	checkResult(result, testkit.Rows(expected...))
+}
+
 // https://github.com/pingcap/tidb/pull/6249 fixes the following two test cases.
 func (s *testStateChangeSuite) TestWriteOnlyWriteNULL(c *C) {
 	sqls := make([]sqlWithErr, 1)
diff --git a/ddl/ddl_api.go b/ddl/ddl_api.go
index 6ac34701538f2..70109e9214981 100644
--- a/ddl/ddl_api.go
+++ b/ddl/ddl_api.go
@@ -1457,7 +1457,22 @@ func modifiable(origin *types.FieldType, to *types.FieldType) error {
 			return nil
 		}
 	case mysql.TypeEnum:
-		return errUnsupportedModifyColumn.GenWithStackByArgs("modify enum column is not supported")
+		if origin.Tp == to.Tp {
+			if len(to.Elems) < len(origin.Elems) {
+				msg := fmt.Sprintf("the number of enum column's elements is less than the original: %d", len(origin.Elems))
+				return errUnsupportedModifyColumn.GenWithStackByArgs(msg)
+			}
+			for index, originElem := range origin.Elems {
+				toElem := to.Elems[index]
+				if originElem != toElem {
+					msg := fmt.Sprintf("cannot modify enum column value %s to %s", originElem, toElem)
+					return errUnsupportedModifyColumn.GenWithStackByArgs(msg)
+				}
+			}
+			return nil
+		}
+		msg := fmt.Sprintf("cannot modify enum type column's to type %s", to.String())
+		return errUnsupportedModifyColumn.GenWithStackByArgs(msg)
 	default:
 		if origin.Tp == to.Tp {
 			return nil