if ct.LengthValue.Valid {
		return ct.LengthValue.Int64, true
	}
	return ct.SQLColumnType.Length()
}

// DecimalSize returns the scale and precision of a decimal type.
func (ct ColumnType) DecimalSize() (precision int64, scale int64, ok bool) {
	if ct.DecimalSizeValue.Valid {
		return ct.DecimalSizeValue.Int64, ct.ScaleValue.Int64, true
	}
	return ct.SQLColumnType.DecimalSize()
}

	ColumnType() (columnType string, ok bool) // varchar(64)
	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 {

	type UserMigrateColumn struct {
		ID       uint
		Name     string
		Salary   float64
		Birthday time.Time `gorm:"precision:4"`
	}

	DB.Migrator().DropTable(&UserMigrateColumn{})

	DB.AutoMigrate(&UserMigrateColumn{})

	type UserMigrateColumn2 struct {
		ID                  uint
		Name                string    `gorm:"size:128"`
		Salary              float64   `gorm:"precision:2"`