建立四个表，分别是学生表，课程表，成绩表和教师信息表
插入信息：
题目：
1、 查询Student表中的所有记录的Sname、Ssex和Class列
select Sname,Ssex,Class from Student
2、 查询教师所有的单位即不重复的Depart列。
select distinct Depart from Teacher
3、 查询Student表的所有记录。
select * from student
4、 查询Score表中成绩在60到80之间的所有记录。
select * from Score where Degree between 60 and 80
5、 查询Score表中成绩为85，86或88的记录。
select * from Score where Degree in (85,86,88)
6、 查询Student表中“95031”班或性别为“女”的同学记录。
select * from student where Class = 95031 or Ssex = '女'
7、 以Class降序查询Student表的所有记录。
select * from student order by Class desc
8、 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
9、 查询“95031”班的学生人数。
select COUNT (*) 人数 from student where Class =95031
10、 查询Score表中的最高分的学生学号和课程号。（子查询或者排序）
select Sno,cno from Score where Degree =(select MAX (Degree ) from Score )
11、 查询每门课的平均成绩。
select AVG(Degree) 平均成绩 from Score group by Cno
12、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 like '3%' group by Cno having COUNT (*)>=5
思路：先把score表查询出来，然后用函数avg把score表的平均分查询出来，然后用where条件句把以3开头的课程这个条件筛选出来，
最后用having把5个学生选修这个条件筛选出来
13、查询分数大于70，小于90的Sno列。
select Sno from Score where Degree >70 and Degree <90
14、查询所有学生的Sname、Cno和Degree列。
select sname,cno,degree from score left join student on student.sno=score.sno
15、查询所有学生的Sno、Cname和Degree列。
select cname,sno,degree from score join course on course.cno=score.cno
16、查询所有学生的Sname、Cname和Degree列。
select cname,sname,degree from score join course on course.cno=score.cno join student on student.sno=score.sno
17、 查询“95033”班学生的平均分。
select AVG (Degree ) from Score where Sno in(select Sno from student where Class ='95033')
18、 假设使用如下命令建立了一个grade表：
create table grade(low int(3),upp int(3),rank char(1))
insert into grade values(90,100,’A’)
insert into grade values(80,89,’B’)
insert into grade values(70,79,’C’)
insert into grade values(60,69,’D’)
insert into grade values(0,59,’E’)
现查询所有同学的Sno、Cno和rank列。
19、 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 > any (select Degree from Score where Sno ='105')
20、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。
解1、
select * from Score where Sno in (select Sno from Score where Sno !=(select * from Score where Degree ='91') group by Sno having COUNT (*)>1)
思路：
解2、
select * from Score where Sno in (select Sno from Score where Sno
!=(select * from Score where Degree ='91') group by Sno having COUNT (*)>1)
思路：
21、 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 Cno='3-105' and Degree > any (select Degree from Score where Sno=109)
22、查询和学号为108的同学同年出生的所有学生的Sno、Sname和Sbirthday列。
select Sno,Sname ,Sbrithday from student where YEAR (Sbrithday )= (select YEAR (Sbrithday ) from student where Sno =108)
23、查询“张旭“教师任课的学生成绩。
select * from score where cno in (select cno from course where tno in(select tno from teacher where tname='张旭' ))
24、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))
思路：先把这个题用到的teacher，score，course表查询出来看一下，先用group by和having 把同学人数多于五人的课程代号这个条件筛选出来，
然后再把教这个课程的老师代号查询出来，知道老师的代号之后再把老师的姓名查询出来
25、查询95033班和95031班全体学生的记录。
select * from student where Class in(95033,95031)
26、 查询存在有85分以上成绩的课程Cno.
select distinct Cno from Score where Degree >85
27、查询出“计算机系“教师所教课程的成绩表。
select * from course where tno in (select tno from teacher where 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 * from Teacher where Depart ='计算机系' and Prof not in (select Prof from Teacher where Depart ='电子工程系')
union
select * from Teacher where Depart ='电子工程系' and Prof not in (select Prof from Teacher where Depart ='计算机系')
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 * from Score where Cno ='3-105' and Degree >(select MAX(Degree ) from Score where Cno ='3-245') order by Degree desc
思路：先把score表中课程号是3-245的平均成绩查询出来，然后在查询一下score表中课程号是3-105的并且成绩大于86的，按降序排列
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 * from Score s1 where Sno in(103,109,105) and Cno ='3-105' and exists(
select * from Score s2 where Sno in(103,109,105) and Cno ='3-245' and s1.Sno =s2.Sno and s1.Degree >s2.Degree )
思路：
31、 查询所有教师和同学的name、sex和birthday.
select Tname ,Tsex ,Tbrithday from Teacher
union
select Sname ,Ssex ,Sbrithday from student
32、查询所有“女”教师和“女”同学的name、sex和birthday.
select Tname ,Tsex ,Tbrithday from Teacher where Tsex ='女'
union
select Sname ,Ssex ,Sbrithday from student where Ssex ='女'
33、 查询成绩比该课程平均成绩低的同学的成绩表。
select * from Score s1 where exists (
select Cno,AVG (Degree ) from Score s2 group by Cno having s1.Cno =s2.Cno and s1.Degree <AVG(Degree ) )
34、 查询所有任课教师的Tname和Depart.
解1、
select Tname,Depart from Teacher where exists
(select * from Course where Teacher.Tno =Course.Tno )
解2、
select Tname ,Depart from Teacher where Tno in (select distinct Tno from Course )
解3、
select Tname ,Depart from Course left join Teacher on Teacher.Tno =Course.Tno
35 、 查询所有未讲课的教师的Tname和Depart.
select * from teacher where tno not in (select tno from course )
36、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
37、查询Student表中不姓“王”的同学记录。
select * from student where Sname not like '王%'
38、查询Student表中每个学生的姓名和年龄。
select sname, datediff(YEAR,Sbrithday ,'2014-11-9') 年龄 from student
39、查询Student表中最大和最小的Sbirthday日期值。
select MAX (Sbrithday) 最大值,MIN (Sbrithday ) 最小值 from student
40、以班号和年龄从大到小的顺序查询Student表中的全部记录。
select * from student order by Class desc,Sbrithday asc
41、查询“男”教师及其所上的课程。
select Cno from Course where Tno in(select Tno from Teacher where Tsex = '男')
42、查询最高分同学的Sno、Cno和Degree列。
select Sno,Cno ,Degree from Score where Degree in (select MAX (Degree ) from Score)
43、查询和“李军”同性别的所有同学的Sname.
select Sname from student where ssex= (select Ssex from student where Sname ='李军')
44、查询和“李军”同性别并同班的同学Sname.
select Sname from student where Class in(select Class from student where Sname ='李军')
and Ssex =(select Ssex from student where Sname ='李军')
45、查询所有选修“计算机导论”课程的“男”同学的成绩表。
select * from Score where Cno in(select Cno from Course where Cname ='计算机导论')
and Sno in(select Sno from student where Ssex ='男')