我给出一张表
create table `xxx` (
`id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
`uid` INT NOT NULL DEFAULT 0
)engine = InnoDB;
insert into xxx (`uid`) value (0),(1);

select * from `xxx` where `uid` = 0;
和
select * from `xxx` where `uid` = '';
查询的结果为什么是一样的？