if len(users4) != 0 {
		t.Errorf("should find no user when searching with unexisting credit card, but got %v", len(users4))
	}

	var users5 []User

		constraint, table := m.GuessConstraintInterfaceAndTable(stmt, name)
		if constraint != nil {
			vars := []interface{}{clause.Table{Name: table}}
			if stmt.TableExpr != nil {
				vars[0] = stmt.TableExpr
			}
			sql, values := constraint.Build()
			return m.DB.Exec("ALTER TABLE ? ADD "+sql, append(vars, values...)...).Error
		}
		return nil
	})
}

// DropConstraint drop constraint