ddl: ignore integer zerofill size attribute when changing the column types (#20862)

ddl/column_test.go

@@ -938,7 +938,7 @@ func (s *testColumnSuite) TestModifyColumn(c *C) {
 		err    error
 	}{
 		{"int", "bigint", nil},
-		{"int", "int unsigned", errUnsupportedModifyColumn.GenWithStackByArgs("length 10 is less than origin 11")},
+		{"int", "int unsigned", errUnsupportedModifyColumn.GenWithStackByArgs("can't change unsigned integer to signed or vice versa")},
 		{"varchar(10)", "text", nil},
 		{"varbinary(10)", "blob", nil},
 		{"text", "blob", errUnsupportedModifyCharset.GenWithStackByArgs("charset from utf8mb4 to binary")},

ddl/db_test.go

@@ -4930,3 +4930,22 @@ func init() {
 	domain.SchemaOutOfDateRetryInterval = int64(50 * time.Millisecond)
 	domain.SchemaOutOfDateRetryTimes = int32(50)
 }
+
+// Test issue #20529.
+func (s *testSerialDBSuite) TestColumnTypeChangeIgnoreDisplayLength(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+
+	// Change int to int(3).
+	// Although display length is increased, the default flen is decreased, reorg is needed.
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int)")
+	tk.MustExec("alter table t modify column a int(3)")
+
+	// Change int to bigint(1)
+	// Although display length is decreased, default flen is the same, reorg is not needed.
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int)")
+	tk.MustExec("alter table t modify column a bigint(1)")
+	tk.MustExec("drop table if exists t")
+}

ddl/ddl_api.go

@@ -2706,6 +2706,10 @@ func checkModifyCharsetAndCollation(toCharset, toCollate, origCharset, origColla
 // field length and precision.
 func CheckModifyTypeCompatible(origin *types.FieldType, to *types.FieldType) error {
 	unsupportedMsg := fmt.Sprintf("type %v not match origin %v", to.CompactStr(), origin.CompactStr())
+	var (
+		toFlen     = to.Flen
+		originFlen = origin.Flen
+	)
 	switch origin.Tp {
 	case mysql.TypeVarchar, mysql.TypeString, mysql.TypeVarString,
 		mysql.TypeBlob, mysql.TypeTinyBlob, mysql.TypeMediumBlob, mysql.TypeLongBlob:
@@ -2718,6 +2722,10 @@ func CheckModifyTypeCompatible(origin *types.FieldType, to *types.FieldType) err
 	case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
 		switch to.Tp {
 		case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
+			// For integers, we should ignore the potential display length represented by flen, using
+			// the default flen of the type.
+			originFlen, _ = mysql.GetDefaultFieldLengthAndDecimal(origin.Tp)
+			toFlen, _ = mysql.GetDefaultFieldLengthAndDecimal(to.Tp)
 		default:
 			return errUnsupportedModifyColumn.GenWithStackByArgs(unsupportedMsg)
 		}
@@ -2756,9 +2764,8 @@ func CheckModifyTypeCompatible(origin *types.FieldType, to *types.FieldType) err
 			return errUnsupportedModifyColumn.GenWithStackByArgs(unsupportedMsg)
 		}
 	}
-
-	if to.Flen > 0 && to.Flen < origin.Flen {
-		msg := fmt.Sprintf("length %d is less than origin %d", to.Flen, origin.Flen)
+	if toFlen > 0 && toFlen < originFlen {
+		msg := fmt.Sprintf("length %d is less than origin %d", toFlen, originFlen)
 		return errUnsupportedModifyColumn.GenWithStackByArgs(msg)
 	}
 	if to.Decimal > 0 && to.Decimal < origin.Decimal {

ddl/ddl_worker_test.go

@@ -723,7 +723,7 @@ func (s *testDDLSuite) TestCancelJob(c *C) {
 	// modify column
 	col.DefaultValue = "1"
 	updateTest(&tests[15])
-	modifyColumnArgs := []interface{}{col, col.Name, &ast.ColumnPosition{}, byte(0)}
+	modifyColumnArgs := []interface{}{col, col.Name, &ast.ColumnPosition{}, byte(0), uint64(0)}
 	doDDLJobErrWithSchemaState(ctx, d, c, dbInfo.ID, tblInfo.ID, test.act, modifyColumnArgs, &test.cancelState)
 	c.Check(checkErr, IsNil)
 	changedTable = testGetTable(c, d, dbInfo.ID, tblInfo.ID)