【day2】mysql主键、外键、自增

create table class(cid int primary key auto_increment,caption char(20) not null);　　#创建class表
　　
insert into class(caption) values(‘三年二班‘),(‘一年三班‘),(‘三年一班‘);　　　　　　　　　　#插入班级数据
　　
create table student(sid int primary key auto_increment,sname char(20) not null,gender enum(‘男‘,‘女‘),class_id int not null,constraint foreign key(class_id) references class(cid) on delete cascade on update cascade)　　　　　　　　#创建学生表，班级id关联到class表的cid

insert into student(sname,gender,class_id) values(‘钢蛋‘,‘女‘,1),(‘钢锤‘,‘女‘,1),(‘山炮‘,‘男‘,2) #插入数据

create table teacher(tid int primary key auto_increment,tname char(20) not null);　　　　　　

insert into teacher(tname) values(‘波多‘)，(‘苍井‘)，(‘饭岛爱‘)；

create table course(cid int primary key auto_increment,cname char(20) not null,teach_id int not null,constraint foreign key(teach_id) references teacher(tid) on delete cascade on update cascade);

insert into course(cname,teach_id) values(‘生物‘,1)，(‘体育‘,1)，(‘物理‘,2)；

create table score(sid int primary key auto_increment,student_id int not null,course_id int not null,number int(3) not null,constraint foreign key(student_id) references student(sid) on delete cascade on update cascade,constraint foreign key(course_id) references course(cid) on delete cascade on update cascade);

insert into course values(1,1,1,60),(2,1,2,59),(3,2,2,100)；