When you enter a new record or update an existing record in a form, and you leave a field empty which is bound to a database column which requires input, then you will see a message complaining about the empty field.
当您在表单中添加一条新的记录或更新一条现有记录，如果将一个字段留空，但该字段与一个必填的数据库列相对应，您将会看到一个关于空字段的提醒信息。