dialects/dialect.go

@@ -163,7 +163,7 @@ func (db *Base) DropIndexSQL(tableName string, index *schemas.Index) string {
 
 func (db *Base) ModifyColumnSQL(tableName string, col *schemas.Column) string {
 	s, _ := ColumnString(db.dialect, col, false)
-	return fmt.Sprintf("alter table %s MODIFY COLUMN %s", tableName, s)
+	return fmt.Sprintf("ALTER TABLE %s MODIFY COLUMN %s", tableName, s)
 }
 
 func (b *Base) ForUpdateSQL(query string) string {

dialects/mssql.go

@@ -368,6 +368,11 @@ func (db *mssql) DropTableSQL(tableName string) (string, bool) {
 		"DROP TABLE \"%s\"", tableName, tableName), true
 }
 
+func (db *mssql) ModifyColumnSQL(tableName string, col *schemas.Column) string {
+	s, _ := ColumnString(db.dialect, col, false)
+	return fmt.Sprintf("ALTER TABLE %s ALTER COLUMN %s", tableName, s)
+}
+
 func (db *mssql) IndexCheckSQL(tableName, idxName string) (string, []interface{}) {
 	args := []interface{}{idxName}
 	sql := "select name from sysindexes where id=object_id('" + tableName + "') and name=?"

integrations/session_schema_test.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"xorm.io/xorm/schemas"
 )
 
 func TestStoreEngine(t *testing.T) {
@@ -396,3 +397,26 @@ func TestSync2_Default(t *testing.T) {
 	assertSync(t, new(TestSync2Default))
 	assert.NoError(t, testEngine.Sync2(new(TestSync2Default)))
 }
+
+func TestModifyColum(t *testing.T) {
+	type TestModifyColumn struct {
+		Id       int64
+		UserId   int64  `xorm:"default(1)"`
+		IsMember bool   `xorm:"default(true)"`
+		Name     string `xorm:"char(10)"`
+	}
+
+	assert.NoError(t, PrepareEngine())
+	assertSync(t, new(TestModifyColumn))
+
+	alterSQL := testEngine.Dialect().ModifyColumnSQL("test_modify_column", &schemas.Column{
+		Name: "name",
+		SQLType: schemas.SQLType{
+			Name: "VARCHAR",
+		},
+		Length:   16,
+		Nullable: false,
+	})
+	_, err := testEngine.Exec(alterSQL)
+	assert.NoError(t, err)
+}