MySQL查询实例

数据库内容：

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) from Score where Cno in (select Cno from Score group by Cno having count(*)>5) and Cno like '3%' group by Cno

select avg(Degree) from Score where Cno like '3%' group by Cno having count(*)>5

查询选修“3-105”课程的成绩高于“109”号同学成绩的所有同学的记录。

select * from Score where Cno ='3-105' and Degree>(select Degree from Score where Sno = '109' and Cno = '3-105')

查询成绩高于学号为“109”、课程号为“3-105”的成绩的所有记录。

select * from Score where Degree >(select Degree from Score where Sno = '109' and Cno = '3-105')

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。

理解1
select * from Score a where Sno in (select Sno from Score group by Sno having count(*)>1 ) and Degree not in (select max(Degree) from Score b where b.Cno =
 a.Cno)
 理解2
select * from Score a where Sno in (select Sno from Score group by Sno having count(*)>1 ) and Degree not in (select max(Degree) from Score a where Sno in 
(select Sno from Score group by Sno having count(*)>1 ))

查询所有“女”教师和“女”同学的name、sex和birthday.

select Sname,Ssex,Sbirthday from Student where Ssex='女' union
select Tname,Tsex,Tbirthday from Teacher where Tsex='女'

查询Student表中最大和最小的Sbirthday日期值。

select max(Sbirthday) from Student union select min(Sbirthday) from Student

查询Student表中不姓“王”的同学记录。

select * from Student where Sno not in(select Sno from Student where Sname like '王%')

查询和“李军”同性别并同班的同学Sname.

select Sname from Student where Ssex = (select Ssex from Student where Sname='李军') and Class=(select Class from Student where Sname = '李军')