选修所有课程的学生信息

create table students(
    sid int not null primary key auto_increment,
    sname char(4) not null,
    ssex char(2) not null
);

create table course(
    cid int not null primary key auto_increment,
    cname varchar(64) not null,
);

create table student_course(
    sid int not null,
    cid int not null,
    constraint for_key_sid foreign key(sid) references students(sid),
    constraint for_key_cid foreign key(cid) references course(cid),
    primary key(sid,cid)
);

查询选修了所有课程的学生的学号和姓名：

select sid,sname from students where not exists(
    select sid from course where not exists(
        select * from student_course where sid = students.sid and cid = course.cid
    )
);