数据库 查询方法详解 以学生老师信息表为例

create table Student--3rd再次执行
(
   Sno int primary key not null,--学号主键
   Sname varchar(50) not null,--学生姓名
   Ssex varchar(50) not null,--学生性别
   Sbirthday datetime,--出生年月
   Class int--班级
)
truncate table Student--清空表格
insert into Student values(108,‘曾华‘,‘男‘,‘1977-09-01‘,95033)
insert into Student values(105,‘匡明‘,‘男‘,‘1975-10-02‘,95031)
insert into Student values(107,‘王丽‘,‘女‘,‘1976-01-23‘,95033)
insert into Student values(101,‘李军‘,‘男‘,‘1976-02-20‘,95033)
insert into Student values(109,‘王芳‘,‘女‘,‘1975-02-10‘,95031)
insert into Student values(103,‘陆君‘,‘男‘,‘1974-06-03‘,95031)
select *from Student
delete from Student



create table Course--2nd其次执行
(  
   Cno char(5) primary key not null,--课程号主键
   Cname Varchar(10)not null,--课程名称
   Tno Varchar(50) not null--教工编号（外码）
   foreign key(Tno)
   references Teacher (Tno),
)
insert into Course values(‘3-105‘,‘计算机导论‘,‘825‘)
insert into Course values(‘3-245‘,‘操作系统‘,‘804‘)
insert into Course values(‘6-166‘,‘数字电路‘,‘856‘)
insert into Course values(‘9-888‘,‘高等数学‘,‘831‘)
select *from Course
delete from Course



create table Score--4th最后执行
(
  Sno int not null, --学号（外码）
  Cno Char(5) not null,--课程号（外码）
  Degree Decimal(4,1),--成绩
  foreign key(Sno)
  references Student(Sno),--学号（外码）
  foreign key(Cno)
  references Course(Cno),--课程号（外码）
  primary key(Sno,Cno)
)
insert into Score values(103,‘3-245‘,86)
insert into Score values(105,‘3-245‘,75)
insert into Score values(109,‘3-245‘,68)
insert into Score values(103,‘3-105‘,92)
insert into Score values(105,‘3-105‘,88)
insert into Score values(109,‘3-105‘,76)

insert into Score values(101,‘3-105‘,64)
insert into Score values(107,‘3-105‘,91)
insert into Score values(108,‘3-105‘,78)
insert into Score values(101,‘6-166‘,85)
insert into Score values(107,‘6-166‘,79)
insert into Score values(108,‘6-166‘,81)
delete from Score

  
  
 create table Teacher--1st首先执行
(  
    Tno varchar(50) primary key not null,--教工编号（主码）
    Tname varchar(50)not null,--教工姓名
    Tsex varchar(50)not null,--教工性别
    Tbirthday datetime,--教工出生年月
    Prof varchar(50),--职称
    Depart Varchar(10)not null--教工所在部门
)
insert into Teacher values(804,‘李诚‘,‘男‘,‘1958-12-02‘,‘副教授‘,‘计算机系‘)
insert into Teacher values(856,‘张旭‘,‘男‘,‘1969-03-12‘,‘讲师‘,‘电子工程系‘)
insert into Teacher values(825,‘王萍‘,‘女‘,‘1972-05-05‘,‘助教‘,‘计算机系‘)
insert into Teacher values(831,‘刘冰‘,‘女‘,‘1977-08-14‘,‘助教‘,‘电子工程系‘)

select *from Student
select *from Course
select *from Teacher
select *from Score
delete from Teacher



--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,Degree desc;

--9.查询“95031”班的学生人数。--聚合函数，针对数据列，计算求和或者计数等一系列算数性，返回结果是一个数值
--SUM(数值类型列) AVG(数值类型列) MAX(数值类型列) MIN(数值类型列) COUNT(*)
select COUNT(*) from Student where Class=95031
select MAX(Degree) as maxfen ,MIN(Degree) minfen from Score where Cno=‘3-105‘--as起别名

--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);
select top 1 *from Score order by Degree desc--从大到校排序再取第一行

--11.查询‘3-105’号课程的平均分。
Select AVG(Degree) from Score where Cno=‘3-105‘;
--查询每门课的平均成绩--分组和聚合结合的时候，先分组，然后对每一组分别进行聚合
Select AVG(Degree) from Score group by Cno;--先按Cno分组，在对Cno聚合

--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 x.Cno ,avg(x.Degree) from Score x where Cno like ‘3%‘ and 5<(select count (*) from Score y where x.Cno = y.Cno) group by x.Cno
select Cno,AVG(Degree) from Score where Cno like ‘3%‘ group by Cno having COUNT(*)>=5--筛选分组完了再对每一组进行AVG聚合，分完组之后相当于只剩下分完组的列
select Cno,AVG(Degree) as degreess from Score where Cno like ‘3%‘ group by Cno having COUNT(*)>=1 order by degreess--order by理解为最后才执行

--13.查询最低分大于70，最高分小于90的Sno列。
select x.Sno from Score x where 70 < (select MIN(y.Degree) from Score y where x.Sno=y.Sno)and 90>(select max(z.Degree) from Score z where x.Sno=z.Sno);
select Sno from Score where Degree >70 and Degree <90--分数大于70，小于90的Sno列

--14.查询所有学生的Sname、Cno和Degree列。--表连接，一定有主外键关系：都好隔开两个表形成笛卡尔积，再进行where筛选，通过表主外键关系筛选，where只是个筛选条件
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。--left right
select Sno,Cname,Degree from Score inner join course on Score.Cno=Course.Cno--不写默认也是有inner
select Student.Sno,Sname,Ssex,Student.Class,Score.Sno,Score.Cno,Score.Degree from Student left join Score on Student.Sno=Score.Sno--left join左表显示全，右表有关系的显示，没有的显示为空
select Student.Sno,Sname,Ssex,Student.Class,Score.Sno,Score.Cno,Score.Degree from Student right join Score on Student.Sno=Score.Sno
select Sno,(select Cname from Course where Score.Cno=Course.Cno)as Lesson,Degree from Score--子查询

--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 Score.Cno=Course.Cno

--17.查询“95033”班所选课程的平均分。
select AVG(degree)from Student join Score on Student.Sno=Score.Sno and Class=‘95033‘



--18.★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))
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 *from grade
--现查询所有同学的Sno、Cno和rank列。（三种方法）
select Sno,Cno,Degree,[rank] from Score,grade where Degree between low and upp order by [rank]
select Sno,Cno,Degree,[rank] from Score join  grade on Degree between low and upp order by [rank]--on后面加筛选条件
select Sno,Cno,(select [rank] from grade where Score.Degree between low and upp) as LV from Score order by Degree desc--子查询得到的结果必须唯一



--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>(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。select x.* from Score x where Degree<(select MAX(y.Degree) from Score y where  y.Sno=x.Sno)
select * from score as a where sno in(select sno from score group by sno having COUNT(*)>1 )and
degree <(select MAX(degree) from score as b where b.cno = a.cno group by cno)--去掉每门课的最高分

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 group by Cno having b.Cno=a.Cno)--去掉每门课的最高分

select *from Score where Sno in(select Sno from Score group by Sno having COUNT(*)>1) and 
Degree not in(select MAX(Degree) from Score where Sno in(select Sno from Score group by Sno having COUNT(*)>1))--除去全部课程中的最高分

select *from Score a where Degree not in (select MAX(Degree) from Score b group by Cno having b.Cno=a.Cno)--查询除了每门课最高分之外的其他学生分数信息
--a.Con=b.Con是比较同一门课程（Con）的条件下筛选的，相当于在课程名称相同的情况下比较分数，除去每一门课程的最高分



--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 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 Sno =‘108‘

--23.查询“张旭“教师任课的学生成绩。
select degree from Score where Cno = (select Cno from Course where Tno = (select Tno from Teacher where Tname = ‘张旭‘)) 
select degree from Score join Course on Score.Cno=Course.Cno join Teacher on Course.Tno=Teacher.Tno 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(Cno)>=5))

--25.查询95033班和95031班全体学生的记录。
select*from student inner join Score on Student.Sno=Score.Sno where Class in(95033,95031)

--26.查询存在有85分以上成绩的课程Cno.
select 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 Score where Cno in( select Cno from Course where Tno in (select Tno from Teacher where Depart=‘计算机系‘))
select Sno,Score.Cno,Degree from Score join Course on Score.Cno=Course.Cno join Teacher on Course.Tno=Teacher.Tno 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 Tname,Prof from Teacher 

--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

--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 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 sname,ssex,sbirthday from student
union
select Tname,Tsex,Tbirthday from Teacher 

--32.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‘

--33.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 a.degree<(select AVG(degree) from score as b where a.cno = b.cno  group by cno)
select * from score as a where a.degree<(select AVG(degree) from score as b  group by cno having a.cno = b.cno)
select * from Score where Degree < any (select AVG(Degree) from Score group by Cno)

--34.查询所有任课教师的Tname和Depart.
select Tname,Depart from Teacher where Tno in(select Tno from Course)  

--35.查询所有未讲课的教师的Tname和Depart. 
select Tname,Depart from Teacher where Tno in(select Tno from Course where Cno not in(select Cno from Score group by Cno))

--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,nianling=(select DATEDIFF(YEAR,Sbirthday,GETDATE())) from Student

--39.★查询Student表中最大和最小的Sbirthday日期值。
select max(Sbirthday)as [max],MIN(Sbirthday) as[min] 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,Sbirthday

--41、查询“男”教师及其所上的课程。
select Teacher.Tno,Tname,Tsex,Cname,Cno from Teacher join Course on Teacher.Tno=Course.Tno where Tsex=‘男‘

--42、查询最高分同学的Sno、Cno和Degree列。
select *from Score where Degree=(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 Ssex=(select Ssex from Student where Sname=‘李军‘) and Class=(select Class 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 Sno in(select Sno from Student where Ssex=‘男‘) and Cno=(select Cno from Course where Cname=‘计算机导论‘);