sql数据库查询

简单查询：
一、投影
select * from 表名
select 列1,列2... from 表名
select distinct 列名 from 表名
二、筛选
select top 数字 列|* from 表名
（一）等值与不等值
select * from 表名 where 列名=值
select * from 表名 where 列名!=值
select * from 表名 where 列名>值
select * from 表名 where 列名<值
select * from 表名 where 列名>=值
select * from 表名 where 列名<=值

（二）多条件与范围
select * from 表名 where 条件1 and|or 条件2 ...
select * from 表名 where between ... and ...
select * from 表名 where 列 in (值列表)

（三）模糊查询 like % _
select * from 表名 where 列 like '%_....'

三、排序
select * from 表名 where 条件 order by 列名 ASC|DESC,列名 ASC|DESC

四、分组：
统计函数（聚合函数）
count(), max(), min(), sum(), avg()

count()统计总行数
count(*)得到所有的行数
count(列)得到该列中所有非null个数。
select COUNT(*) from car where Brand='b003'

max(列) 这一列的最大，min(列)这一列的最小
select min(price) from car

sum(列)这一列的和，avg(列)这一列的平均
select AVG(price) from car

group by ...having...

1.group by后面跟的是列名。
2.一旦使用group by分组了，则select和from中间就不能用*，只能包含两类东西一类是：group by 后面的列名，另一类是统计函数
select Oil,avg(price) from Car group by oil
对于统计函数生成的列，默认是无列名，可以通过下面的方法指定列名。
select Oil as 油耗,COUNT(*) as 数量,avg(price) 均价 from Car group by oil

having后面一般跟得是统计函数。它用来对分组后的数据进一步筛选。


复杂查询：
一、连接查询
把多个表的列合在一个界面视图中。
思想：1.生成笛卡尔积。2.对笛卡尔积进行筛选。3.选择列进行显示。
select 表1.列1,表1.列2,表2.列1,表2.列2…… from 表1,表2 where 表1.列=表2.列

select * from 表1 
join 表2 on 表1.列=表2.列
join 表3 on 表2.列=表3.列

左连(left join)，右连(right join),全连(full join)

二、联合查询
把多个表的行合在一个界面视图中。
用union把两个查询组合在一起。要求是这两个查询的列要一一对应。

三、子查询（嵌套查询）
(一)无关子查询：
至少是两层查询，在外层查询的里面再写查询。
里层查询为外层查询提供查询的中间内容。

create database test
go
use test
go
create table student
(
    --学号
    sno varchar(3) not null primary key,
    --姓名
    sname varchar(4) not null,
    --性别
    ssex varchar(2) not null,
    --出生年月
    sbirthday datetime,
    --所在班级
    class varchar(5)
)
go
create table teacher
(
    --教工编号
    tno varchar(3) not null primary key,
    --教工姓名
    tname varchar(4) not null,
    --教工性别
    tsex varchar(2) not null,
    --教工出生日期
    tbirthday datetime,
    --职称
    prof varchar(6),
    --所在部门
    depart varchar(10)
)
go
create table course
(
    --课程号
    cno varchar(5) not null primary key,
    --课程名称
    cname varchar(10) not null,
    --教工编号
    tno varchar(3) references teacher(tno)
)
go
create table score
(
    --学号
    sno varchar(3) not null references student(sno),
    --课程号
    cno varchar(5) not null references course(cno),
    --成绩
    degree decimal(4,1)
)
go


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')

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','1958-08-14','助教','电子工程系')

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')


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')

select * from student
select * from teacher
select * from course
select * from score



--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(*) 数量 from student where class=95031
--10、查询Score表中的最高分的学生学号和课程号。
 select sno,cno from score  where degree=(select MAX(degree)分数 from score)
--11、查询‘3-105’号课程的平均分。
select AVG(degree) from score where cno='3-105'
--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 =
(select cno from score group by cno having count(*)>=5)) and cno like '3%'


select cno,count(*),AVG(degree) from score where cno like '3%' group by cno having COUNT(*)>=5

--13、查询最低分大于70，最高分小于90的Sno列
select sno,MAX(degree),MIN(degree) from score group by sno having   MAX(degree)<90 and MIN(degree)>70
--14、查询所有学生的Sname、Cno和Degree列。
select sname,cno,degree from
 student join score on student.sno=score.sno

--15、查询所有学生的Sno、Cname和Degree列。p
select sno ,cname,degree from score  join course on score.cno=course.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”班所选课程的平均分。
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,upp  int,rank  varchar(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。
select sno,cno,rank from score join grade on score.degree>grade.low and score.degree < grade.upp
--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 degree from score where cno='3-105' and sno='109'--76
select * from score where cno='3-105' and
 degree>(select degree from score where cno='3-105' and sno='109')

--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 * from score
 select sno  from score group by sno having  count(*)>1--有歧义


--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 year(sbirthday) from student  where sno=108
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 tno from teacher where tname='张旭'

select cno from course where tno=(select tno from teacher where tname='张旭')

select degree 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 cno from score group by cno having COUNT(*)>5
select tno from course where cno=(select cno from score group by cno having COUNT(*)>5)
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
union
select *from student where class=95031
--26、查询存在有85分以上成绩的课程Cno.
select cno from score where degree >85
select cname from course  where cno in (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 tno from teacher where depart ='计算机系'
 select cno from course where tno in (select tno from teacher where depart ='计算机系') 
 select degree from score  where cno in ( select cno 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 prof from teacher where (depart='计算机系' or depart='电子工程系')
select prof from teacher group by prof  having COUNT(*)=1
select tname ,prof  from teacher where  prof in (select prof from teacher group by prof  having COUNT(*)=1)and prof in (select prof from teacher where (depart='计算机系' or depart='电子工程系'))
--的Cno、Sno和Degree,并按Degree从高到低次序排序。
select degree from score where cno='3-105'
select MAX(degree) from score where cno='3-245'
select degree from score where degree in (select degree from score where cno='3-105') and degree>
(select MAX(degree) from score where cno='3-245') 
select * from score  where degree in (select degree from score where cno='3-105') and degree>
(select MAX(degree) from score where cno='3-245')  order by degree desc


--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.

--31、查询所有教师和同学的name、sex和birthday.
select * from student  
select * from teacher 
select * from course 
select * from score 

select sname 姓名, ssex 性别,sbirthday 生日 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
select * from score 
select avg(degree) from score  group by cno

select degree from score group by cno

--insert into teacher values('888','aaa','v','2005.1.1','a','a')
select cno from course where cno not in (select cno from score )
select * from teacher
select cno from score 
select tname ,depart from teacher join course on teacher.tno=course.tno  left join score on course.cno=score .cno where course . cno=(select cno from course where cno not in (select cno from score ))
--36、查询至少有2名男生的班号。
--insert into student values('110','aaa','a','2005.1.1','95000')
select class from student group by class having count('男')>=2
--37、查询Student表中不姓“王”的同学记录。
select sname from student where sname like '王%'
select * from student where sname not in (select sname from student where sname like '王%')
--38、查询Student表中每个学生的姓名和年龄。
select sname 姓名,YEAR(getdate())-year(sbirthday) 年龄 from student 

--39、查询Student表中最大和最小的Sbirthday日期值。
select MAX(sbirthday) 最大生日,MIN(sbirthday) 最小生日 from student
select * 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 desc
--41、查询“男”教师及其所上的课程。
select * from teacher where tsex='男'
select tname, cname from course join teacher  on course .tno=teacher.tno where tsex='男'  
--42、查询最高分同学的Sno、Cno和Degree列。
select MAX(degree) from score
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 ssex from student where sname='李军'
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 * from student
select class from student  where sname='李军'
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 student
select * from course
select * from score
select degree from student  join score on student .sno=score.sno join course on score .cno=course.cno where cname='计算机导论' and ssex='男'