数据库练习题1-25题

--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。--distinct 去除重复
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。--降序：desc 升序：默认asc
select * from Score order by Cno,Degree desc 

--9、 查询“95031”班的学生人数。
select COUNT(*)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)--子查询法

select top 1 Sno,Cno from Score  order by Degree desc --排序法，用Top

--11、 查询每门课的平均成绩。
select Cno,AVG(Degree) 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 Cno,AVG(Degree) from Score  group by Cno having COUNT(*)>5 and Cno like '3%'

 
--13、查询分数大于70，小于90的Sno列。--between/and 是包含，是大于等于，所以这里不能用，要用>,<
select Sno from Score  where Degree > 70 and Degree < 90

--0014、查询所有学生的Sname、Cno和Degree列。注：如果查询2个表中同样sname 需要分别写出Studen.Sname和Score.Sname 
select Sname,Degree,Cno  from Student join Score on Student.Sno=Score.Sno --把2个表格联合做法
select Sname,Cno,Degree from Student,Score where Student.Sno=Score.Sno

--15.查询所有学生的Sno、Cname和Degree列。
select Student.Sno,Cname,Degree from Student join Score on Student.Sno=Score.Sno join Course on  Course.Cno=Score.Cno 

--16、查询所有学生的Sname、Cname和Degree列。
select Sname,Cname,Degree from Student join Score on Student.Sno=Score.Sno join Course on  Course.Cno=Score.Cno


--17、 查询“95033”班学生的平均分。
 select AVG(Degree)  from Student join Score on Student.Sno=Score.Sno group by class having Class='95033' --先把2个图拼起来再分组，再求平均值
 
-0018假设使用如下命令建立了一个grade表：
create table grade
(
  low int,
  upp int,
  rank char(1),
)  
go
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')

select Sno,Cno,RANK from Score,grade where Degree between low and upp --变量可以直接做范围low/upp

--0019、  查询选修“3-105”课程的成绩并且高于“109”号同学成绩的所有同学的记录。
select Degree from Score where Cno = '3-105' and Degree>(
select Degree from Score where Sno = '109' and Cno ='3-105')

--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。
1.找同学
select sno from score group by sno having COUNT(*)>1
2.找最高分
select MAX(degree) from score where sno in(select sno from score group by sno having COUNT(*)>1)
3.去掉最高分
select sno from score where degree !=(select MAX(degree) from score where sno in(select sno from score group by sno having COUNT(*)>1)) group by sno having COUNT(*)>1 
4.找非最高分学生的信息
select * from score where sno in (select sno from score where degree !=(select MAX(degree) from score where sno in(select sno from score group by sno having COUNT(*)>1)) group by sno having COUNT(*)>1)

--21、 查询成绩高于学号为“109”并且课程号为“3-105”的成绩的所有记录。
select Sno,Cno,Degree from Score where Degree > (select Degree from Score where Sno=109 and Cno='3-105')

--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,Sbirthday from Student where YEAR( Sbirthday) = (select YEAR( Sbirthday) from Student where Sno='108') 

--23、查询“张旭“教师任课的学生成绩。
 select * from Score where Cno = (select Cno from Course where Tno= (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 =( select Tno from Course where Cno = ( select Cno from Score group by Cno having COUNT(*)>5))

--25、查询95033班和95031班全体学生的记录。
select * from Student where Class = '95033' or Class = '95031'