day46 作业

# 班级表
create table class(
	cid int primary key auto_increment,
    caption char(16)
);
# 学生表
create table student(
	sid int primary key auto_increment,
    sname char(16),
    gender enum('male','female'),
    class_id int ,
    foreign key(class_id) references class(cid)
    on update cascade
    on delete cascade
);
# 老师表
create table teacher(
	tid int primary key auto_increment,
    tname char(16)
);
# 课程表
create table course(
	cid int primary key auto_increment,
    cname char(16),
    teacher_id int,
    foreign key(teacher_id) references teacher(tid)
    on update cascade
    on delete cascade
);
# 成绩表
create table gender(
	sid int primary key auto_increment,
    student_id int,
    course_id int,
    number int,
    foreign key(student_id) references student(sid)
    on update cascade
    on delete cascade,
    foreign key(course_id) references course(cid)
    on update cascade
    on delete cascade
);