和另外一張表產生關係

1.節省空間

2.約束，保持一致性

create table userinfo(

　　uid int auto_increment priority key,

　　name varchar(32),

　　department_id int,

　　constrait fk_user_depar foreign key ("department_id",) references department("id")　　# 外來鍵

)engine=innodb default charset=utf-8;

creat table department(

　　id int auto_increment priority key,

　　title char(15)

)engine=innodb default charset=utf-8;