primary key

•id int primary key

•constraint pk_temp_id primary key(id)

•alter刪除主鍵約束 ：alter table temp drop primary key;  

•alter添加主鍵 ：alter table temp add primary key(name, pwd);  

•alter修改列爲主鍵 ：alter table temp modify id int primary key;

•

•  設置主鍵自增：auto_increment

•id int auto_increment primary key,