alterColumn = true
			}
		}
	}

	// check nullable
	if nullable, ok := columnType.Nullable(); ok && nullable == field.NotNull {
		// not primary key & database is nullable
		if !field.PrimaryKey && nullable {
			alterColumn = true
		}
	}

	// check default value
	if !field.PrimaryKey {

		return ct.DecimalSizeValue.Int64, ct.ScaleValue.Int64, true
	}
	return ct.SQLColumnType.DecimalSize()
}

// Nullable reports whether the column may be null.
func (ct ColumnType) Nullable() (nullable bool, ok bool) {
	if ct.NullableValue.Valid {
		return ct.NullableValue.Bool, true
	}
	return ct.SQLColumnType.Nullable()
}

// Unique reports whether the column may be unique.
func (ct ColumnType) Unique() (unique bool, ok bool) {

	PrimaryKey() (isPrimaryKey bool, ok bool)
	AutoIncrement() (isAutoIncrement bool, ok bool)
	Length() (length int64, ok bool)
	DecimalSize() (precision int64, scale int64, ok bool)
	Nullable() (nullable bool, ok bool)
	Unique() (unique bool, ok bool)
	ScanType() reflect.Type
	Comment() (value string, ok bool)
	DefaultValue() (value string, ok bool)
}

type Index interface {
	Table() string

const preparedStmtDBKey = "preparedStmt"

// Config GORM config
type Config struct {
	// GORM perform single create, update, delete operations in transactions by default to ensure database data integrity
	// You can disable it by setting `SkipDefaultTransaction` to true
	SkipDefaultTransaction bool
	// NamingStrategy tables, columns naming strategy
	NamingStrategy schema.Namer
	// FullSaveAssociations full save associations

)

var DB *gorm.DB
var (
	mysqlDSN     = "gorm:gorm@tcp(localhost:9910)/gorm?charset=utf8&parseTime=True&loc=Local"
	postgresDSN  = "user=gorm password=gorm dbname=gorm host=localhost port=9920 sslmode=disable TimeZone=Asia/Shanghai"
	sqlserverDSN = "sqlserver://gorm:LoremIpsum86@localhost:9930?database=gorm"
	tidbDSN      = "root:@tcp(localhost:9940)/test?charset=utf8&parseTime=True&loc=Local"
)

func init() {
	var err error