1、查询所有的课程的名称以及对应的任课老师姓名
select course.cid,course.cname,teacher.tname from course inner join teacher on teacher.tid = course.teacher_id;
2、查询学生表中男女生各有多少人
select gender,count(sid) from student group by gender;
3、查询物理成绩等于100的学生的姓名
select sname from student where sid in (select student_id from score where num=100 and course_id=2);
4、查询平均成绩大于八十分的同学的姓名和平均成绩
select student_id,avg(num) as num from score group by student_id having avg(num) >80;
5、查询所有学生的学号，姓名，选课数，总成绩
select sid,sname,sum,count_score from student inner join (select student_id,sum(num) as sum,count(student_id) as count_score from score group by student_id) as student_sum on student_sum.student_id=student.sid;
6、 查询姓李老师的个数
select count(tname) from teacher where tname like '李%';
7、 查询没有报李平老师课的学生姓名
select sname from student where class_id not in (select cid from course where teacher_id = (select tid from teacher where tname="李平老师"));
8、 查询物理课程比生物课程高的学生的学号select t1.student_id from
(select student_id,num from score where course_id =(select cid from course where cname="物理")) as t1
inner join
(select student_id,num from score where course_id =(select cid from course where cname="生物")) as t2 on t1.student_id = t2.student_id where t1.num>t2.num;
9、 查询没有同时选修物理课程和体育课程的学生姓名select student.sname from student where sid in(
select student_id from score where course_id in (select cid from course where cname="体育" or cname="物理") group by student_id having count(course_id)=1);
10、查询挂科超过两门(包括两门)的学生姓名和班级
、查询选修了所有课程的学生姓名
12、查询李平老师教的课程的所有成绩记录
select sname,course_id,num, from score inner join student on student.sid = score.student_id where course_id in (select cid from course where teacher_id in (select tid from teacher where tname="李平老师")) ;
13、查询全部学生都选修了的课程号和课程名
select student_id from score where course_id in (select cid from course where cname="体育" or cname="物理") group by student_id having count(course_id)=1)
14、查询每门课程被选修的次数
select course_id,count(course_id) from score group by course_id;
15、查询之选修了一门课程的学生姓名和学号
select sid,sname from student where sid=(select student_id from score group by student_id having count(student_id)=1);
16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
select distinct num from score order by num desc;
17、查询平均成绩大于85的学生姓名和平均成绩
select student_id from score group by student_id having avg(num)>85;
18、查询生物成绩不及格的学生姓名和对应生物分数select t1.student_id,student.sname,t1.num from
(select student_id,num from score where course_id = (select cid from course where cname="生物") having num>60)as t1
inner join student on t1.student_id = student.sid;
19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
select sname from student where sid =(
select student_id from score where course_id in (select course.cid from course inner join teacher on course.teacher_id=teacher.tid where teacher.tname="李平老师") group by student_id order by avg(num) desc limit 1);
20、查询每门课程成绩最好的前两名学生姓名
21、查询不同课程但成绩相同的学号，课程号，成绩
22、查询没学过“叶平”老师课程的学生姓名以及选修的课程名称；
23、查询所有选修了学号为1的同学选修过的一门或者多门课程的同学学号和姓名；
24、任课最多的老师中学生单科成绩最高的学生姓名