feat: deal with the unique field migrator (#105)

* feat: deal with the unique field migrator

* feat: rebuild the AlterColumn function

migrator.go

@@ -3,6 +3,7 @@ package mysql
 import (
 	"database/sql"
 	"fmt"
+	"strconv"
 	"strings"
 
 	"gorm.io/gorm"
@@ -49,15 +50,50 @@ func (m Migrator) FullDataTypeOf(field *schema.Field) clause.Expr {
 func (m Migrator) AlterColumn(value interface{}, field string) error {
 	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
 		if field := stmt.Schema.LookUpField(field); field != nil {
+			fullDataType := m.FullDataTypeOf(field)
+			if m.Dialector.DontSupportRenameColumnUnique {
+				fullDataType.SQL = strings.Replace(fullDataType.SQL, " UNIQUE ", " ", 1)
+			}
+
 			return m.DB.Exec(
 				"ALTER TABLE ? MODIFY COLUMN ? ?",
-				clause.Table{Name: stmt.Table}, clause.Column{Name: field.DBName}, m.FullDataTypeOf(field),
+				clause.Table{Name: stmt.Table}, clause.Column{Name: field.DBName}, fullDataType,
 			).Error
 		}
 		return fmt.Errorf("failed to look up field with name: %s", field)
 	})
 }
 
+func (m Migrator) TiDBVersion() (isTiDB bool, major, minor, patch int, err error) {
+	// TiDB version string looks like:
+	// "5.7.25-TiDB-v6.5.0" or "5.7.25-TiDB-v6.4.0-serverless"
+	tidbVersionArray := strings.Split(m.Dialector.ServerVersion, "-")
+	if len(tidbVersionArray) < 3 || tidbVersionArray[1] != "TiDB" {
+		// It isn't TiDB
+		return
+	}
+
+	rawVersion := strings.TrimPrefix(tidbVersionArray[2], "v")
+	realVersionArray := strings.Split(rawVersion, ".")
+	if major, err = strconv.Atoi(realVersionArray[0]); err != nil {
+		err = fmt.Errorf("failed to parse the version of TiDB, the major version is: %s", realVersionArray[0])
+		return
+	}
+
+	if minor, err = strconv.Atoi(realVersionArray[1]); err != nil {
+		err = fmt.Errorf("failed to parse the version of TiDB, the minor version is: %s", realVersionArray[0])
+		return
+	}
+
+	if patch, err = strconv.Atoi(realVersionArray[2]); err != nil {
+		err = fmt.Errorf("failed to parse the version of TiDB, the patch version is: %s", realVersionArray[0])
+		return
+	}
+
+	isTiDB = true
+	return
+}
+
 func (m Migrator) RenameColumn(value interface{}, oldName, newName string) error {
 	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
 		if !m.Dialector.DontSupportRenameColumn {
@@ -173,11 +209,11 @@ func (m Migrator) ColumnTypes(value interface{}) ([]gorm.ColumnType, error) {
 		}
 
 		rawColumnTypes, err := rows.ColumnTypes()
-		
+
 		if err != nil {
 			return err
 		}
-		
+
 		if err := rows.Close(); err != nil {
 			return err
 		}

mysql.go

@@ -40,6 +40,7 @@ type Config struct {
 	DontSupportRenameColumn       bool
 	DontSupportForShareClause     bool
 	DontSupportNullAsDefaultValue bool
+	DontSupportRenameColumnUnique bool
 }
 
 type Dialector struct {
@@ -138,6 +139,10 @@ func (dialector Dialector) Initialize(db *gorm.DB) (err error) {
 			dialector.Config.DontSupportRenameColumn = true
 			dialector.Config.DontSupportForShareClause = true
 		}
+
+		if strings.Contains(dialector.ServerVersion, "TiDB") {
+			dialector.Config.DontSupportRenameColumnUnique = true
+		}
 	}
 
 	// register callbacks