“But there’s an exception with database column types that do not accept empty strings as valid values — such as dates, times and numbers. If you try to insert an empty string into a date or integer column, you’ll likely get a database error, depending on which database you’re using. (PostgreSQL, which is strict, will raise an exception here; MySQL might accept it or might not, depending on the version you’re using, the time of day and the phase of the moon.) In this case, NULL is the only way to specify an empty value. In Django models, you can specify that NULL is allowed by adding null=True to a field.”
— 摘自 Django Book (/en/2.0/chapter06/)
玩MySQL数据类型，还要看时辰，月相…哈哈哈哈
