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 课程 ,Degree from Score--Cname不在Score表中，用子查询时()内的Cname必训as一个新名称



--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

1.查询学号出现两次及以上的学号出来
select Sno from Score group by Sno having COUNT(*)>1
2.查询步骤1中的学号的人的分数
select *from Score  where Sno in(select Sno from Score group by Sno having COUNT(*)>1)
3.查询所有人的分数最高分
select MAX(Degree) from Score where Sno in(select Sno from Score group by Sno having COUNT(*)>1)
4.从步骤2的结果中提出最高分即步骤3的
select *from Score  where Sno in(select Sno from Score group by Sno having COUNT(*)>1)and Degree!=(select MAX(Degree) from Score)





--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 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='109')

--23.查询“张旭“教师任课的学生成绩。
select degree from Score where Cno in (select Cno from Course where Tno in (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)
select *from Student,Score where Class in(95033,95031) and Student.Sno=Score.Sno

--26.查询存在有85分以上成绩的课程Cno.
select distinct Cno from Score where degree>=85;--去重

--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 where Prof not in
(select prof from Teacher where Depart='电子工程系' and Prof in (select Prof from Teacher where Depart='计算机系'))
and Depart in ('计算机系','电子工程系')
--查询两个系中教师相同职称名称，不在这里面的就是除去两个系都有的剩下的，见上面
select prof from Teacher where Depart='电子工程系' and Prof 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

--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.--表连接，union（纵向连接，表1和表2数据类型要对应且列数对应）上下链接，与join on左右相关链接不同
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。--相关子查询--同一门学科的平均分,，每门学科低于自身平均分的
select * from score as a where a.degree<
(select AVG(degree) from score as b where a.cno = b.cno  group by cno)--相当于foreach列出每一门课的平均分
select * from score as a where a.degree<
(select AVG(degree) from score as b  group by cno having a.cno = b.cno)



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

--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 in (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 iN (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');

--至查询student表的第3、4行--分页查询 ★必须要用主键Sno来排除，防止重复
select *from Student
select top 2 *from Student where Sno not in(select top 2 Sno from Student)--第二页，屏蔽掉当前页的前面页的内容，前面top是取屏蔽之后的数据的一页显示条数
--2行为一页
select top 2 *from Student where Sno not in(select top 4 Sno from Student)--第三页