21、查询score中选学多门课程的同学中分数不是所有成绩中最高分成绩的记录。

select * from score  where cno in(select cno from score group by cno having count(1)>1) and degree<>(select max(degree) from score);

24、查询选修某课程的同学人数多于5人的教师姓名。

select t.tname from teacher t join course c on t.tno = c.tno where c.cno in (select cno from score group by cno having count(1)>5);

26、  查询存在有85分以上成绩的课程Cno.

select cno from score where degree in (select degree from score group by degree having degree>85);

27、查询出“计算机系“教师所教课程的成绩表。

select s.* from score s join course c on s.cno = c.cno join teacher t on t.tno = c.tno where t.depart = '计算机系';

28、查询“计算机系”与“电子工程系“不同职称的教师的Tname和Prof。

select t.tname,t.prof from teacher t where t.prof in(select t.prof from teacher t group by t.prof having count(1)=1)

29、查询选修编号为“3-105“课程且成绩至少高于选修编号为“3-245”的同学的Cno、Sno和Degree,并按Degree从高到低次序排序。

select cno,sno,degree from score where cno='3-105'
and degree>=(select min(degree) from score where cno='3-245') order by degree desc;

30、查询选修编号为“3-105”且成绩高于选修编号为“3-245”课程的同学的Cno、Sno和Degree.

select cno,sno,degree from score where cno='3-105' and degree> (select max(degree) from score where cno='3-245');

31、 查询所有教师和同学的name、sex和birthday.

select s.sname,s.ssex,s.sbirthday from student s union select t.tname,t.tsex,t.tbirthday from teacher t;

32、查询所有“女”教师和“女”同学的name、sex和birthday.

select s.sname,s.ssex,s.sbirthday from student s where s.ssex='女' union select t.tname,t.tsex,t.tbirthday from teacher t where t.tsex='女';