MySql 主键

增加主键

create table my_pril

(name varchar(20) not null comment '姓名',

number char(10) primary key comment '学号: itcast +0000 ,不能重复')charset utf8;

复合主键

create table my_pri2

(number char(10) comment '学号 :itcast +000',

course char (10) comment '课程代码: 3901 +0000',

score tinyint unsigned default 60 comment '成绩',

primary key (number,course)

)charset utf8;

追加主键

create table my_pri3

(course char(10) not null comment '课程编号 :00000 ',

name varchar(10) not null comment'课程名字');

alter table my_pri3 modify course char(10) primary key comment '课程编号 :00000 '; 方法1

alter table my_pri3 add primary key (course); 方法2

删除主键

alter table my_pri3 drop primary key ;