// Columns
	AddColumn(dst interface{}, field string) error
	DropColumn(dst interface{}, field string) error
	AlterColumn(dst interface{}, field string) error
	MigrateColumn(dst interface{}, field *schema.Field, columnType ColumnType) error
	// MigrateColumnUnique migrate column's UNIQUE constraint, it's part of MigrateColumn.
	MigrateColumnUnique(dst interface{}, field *schema.Field, columnType ColumnType) error

	expr.SQL = m.DataTypeOf(field)

	if field.NotNull {
		expr.SQL += " NOT NULL"
	}

	if field.HasDefaultValue && (field.DefaultValueInterface != nil || field.DefaultValue != "") {
		if field.DefaultValueInterface != nil {
			defaultStmt := &gorm.Statement{Vars: []interface{}{field.DefaultValueInterface}}
			m.Dialector.BindVarTo(defaultStmt, defaultStmt, field.DefaultValueInterface)