1.以Cno升序、Degree降序查询Score表的所有记录。
select *from score order by cno asc,degree desc
2.查询Score表中至少有5名学生选修的并以3开头的课程的平均分数。
select avg (degree) as '平均分'from score where cno in(
select cno from score group by cno having COUNT(*)>5 and cno like '3%')
3.表连接，在没有共同列时可以进行列与列的比较
ps：select sno,cno,degree,[RANK] from score,grade where degree>low and degree <upp
4.查询score中选学多门课程的同学中分数为非最高分成绩的记录
select *from score where degree <(select MAX(degree)from score where sno in(select sno from score group by sno having COUNT(*)>1))
and sno in (select sno from score group by sno having COUNT(*)>1)
5.查询选修某课程的同学人数多于5人的教师姓名。
select tname from teacher where tno in(select tno from course where cno in (select cno from score group by cno having COUNT(*)>5))
6.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 >any(select degree from score where cno='3-245')order by degree asc
7.查询成绩比该课程平均成绩低的同学的成绩表。
select * from score as a where degree<all(select avg(degree)from score as b where a.cno=b.cno)
8.查询至少有2名男生的班号。
select class from student where ssex ='男' group by class having COUNT(*)>=2
9.以班号和年龄从大到小的顺序查询Student表中的全部记录。
select *, YEAR(GETDATE())-YEAR(sbirthday)as '年龄' from student order by class , YEAR(GETDATE())-YEAR(sbirthday) desc
注意：having 就是group by 的where条件,对group by生成的结果进行筛选，只能跟聚合函数
sql里面as可以简单的理解为重命名，as a对表、对列起别名，起别名就是抓过前面的表过来用