基于实际项目的SQL学习总结

2022-10-04 08:23:47

一个项目涉及到的50个Sql语句(整理版)

/*
标题：一个项目涉及到的50个Sql语句(整理版)
说明：以下五十个语句都按照测试数据进行过测试，最好每次只单独运行一个语句。
*/

--1.学生表
Student(S,Sname,Sage,Ssex) --S 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

--2.课程表 
Course(C,Cname,T) --C --课程编号,Cname 课程名称,T 教师编号
--3.教师表 
Teacher(T,Tname) --T 教师编号,Tname 教师姓名

--4.成绩表 
SC(S,C,score) --S 学生编号,C 课程编号,score 分数

*/

--创建测试数据
create table Student(S varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10))

insert into Student values(‘01‘ , N‘赵雷‘ , ‘1990-01-01‘ , N‘男‘)

insert into Student values(‘02‘ , N‘钱电‘ , ‘1990-12-21‘ , N‘男‘)

insert into Student values(‘03‘ , N‘孙风‘ , ‘1990-05-20‘ , N‘男‘)

insert into Student values(‘04‘ , N‘李云‘ , ‘1990-08-06‘ , N‘男‘)

insert into Student values(‘05‘ , N‘周梅‘ , ‘1991-12-01‘ , N‘女‘)

insert into Student values(‘06‘ , N‘吴兰‘ , ‘1992-03-01‘ , N‘女‘)

insert into Student values(‘07‘ , N‘郑竹‘ , ‘1989-07-01‘ , N‘女‘)

insert into Student values(‘08‘ , N‘王菊‘ , ‘1990-01-20‘ , N‘女‘)

create table Course(C varchar(10),Cname nvarchar(10),T varchar(10))

insert into Course values(‘01‘ , N‘语文‘ , ‘02‘)

insert into Course values(‘02‘ , N‘数学‘ , ‘01‘)

insert into Course values(‘03‘ , N‘英语‘ , ‘03‘)

create table Teacher(T varchar(10),Tname nvarchar(10))

insert into Teacher values(‘01‘ , N‘张三‘)

insert into Teacher values(‘02‘ , N‘李四‘)

insert into Teacher values(‘03‘ , N‘王五‘)

create table SC(S varchar(10),C varchar(10),score decimal(18,1))

insert into SC values(‘01‘ , ‘01‘ , 80)
insert into SC values(‘01‘ , ‘02‘ , 90)

insert into SC values(‘01‘ , ‘03‘ , 99)
insert into SC values(‘02‘ , ‘01‘ , 70)

insert into SC values(‘02‘ , ‘02‘ , 60)
insert into SC values(‘02‘ , ‘03‘ , 80)

insert into SC values(‘03‘ , ‘01‘ , 80)
insert into SC values(‘03‘ , ‘02‘ , 80)

insert into SC values(‘03‘ , ‘03‘ , 80)
insert into SC values(‘04‘ , ‘01‘ , 50)

insert into SC values(‘04‘ , ‘02‘ , 30)
insert into SC values(‘04‘ , ‘03‘ , 20)

insert into SC values(‘05‘ , ‘01‘ , 76)
insert into SC values(‘05‘ , ‘02‘ , 87)

insert into SC values(‘06‘ , ‘01‘ , 31)
insert into SC values(‘06‘ , ‘03‘ , 34)

insert into SC values(‘07‘ , ‘02‘ , 89)
insert into SC values(‘07‘ , ‘03‘ , 98)

go

--1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
--1.1、查询同时存在"01"课程和"02"课程的情况
select a.* , b.score [课程‘01‘的分数],c.score [课程‘02‘的分数] from Student a , SC b , SC c
where a.S = b.S and a.S = c.S and b.C = ‘01‘ and c.C = ‘02‘ and b.score > c.score
--1.2、查询同时存在"01"课程和"02"课程的情况和存在"01"课程但可能不存在"02"课程的情况(不存在时显示为null)(以下存在相同内容时不再解释)
select a.* , b.score [课程"01"的分数],c.score [课程"02"的分数] from Student a
left join SC b on a.S = b.S and b.C = ‘01‘
left join SC c on a.S = c.S and c.C = ‘02‘
where b.score > isnull(c.score,0)

--2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
--2.1、查询同时存在"01"课程和"02"课程的情况
select a.* , b.score [课程‘01‘的分数],c.score [课程‘02‘的分数] from Student a , SC b , SC c
where a.S = b.S and a.S = c.S and b.C = ‘01‘ and c.C = ‘02‘ and b.score < c.score
--2.2、查询同时存在"01"课程和"02"课程的情况和不存在"01"课程但存在"02"课程的情况
select a.* , b.score [课程"01"的分数],c.score [课程"02"的分数] from Student a
left join SC b on a.S = b.S and b.C = ‘01‘
left join SC c on a.S = c.S and c.C = ‘02‘
where isnull(b.score,0) < c.score

--3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩
select a.S , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score
from Student a , sc b
where a.S = b.S
group by a.S , a.Sname
having cast(avg(b.score) as decimal(18,2)) >= 60
order by a.S

--4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩
--4.1、查询在sc表存在成绩的学生信息的SQL语句。
select a.S , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score
from Student a , sc b
where a.S = b.S
group by a.S , a.Sname
having cast(avg(b.score) as decimal(18,2)) < 60
order by a.S
--4.2、查询在sc表中不存在成绩的学生信息的SQL语句。
select a.S , a.Sname , isnull(cast(avg(b.score) as decimal(18,2)),0) avg_score
from Student a left join sc b
on a.S = b.S
group by a.S , a.Sname
having isnull(cast(avg(b.score) as decimal(18,2)),0) < 60
order by a.S

--5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩
--5.1、查询所有有成绩的SQL。
select a.S [学生编号], a.Sname [学生姓名], count(b.C) 选课总数, sum(score) [所有课程的总成绩]
from Student a , SC b
where a.S = b.S
group by a.S,a.Sname
order by a.S
--5.2、查询所有(包括有成绩和无成绩)的SQL。
select a.S [学生编号], a.Sname [学生姓名], count(b.C) 选课总数, sum(score) [所有课程的总成绩]
from Student a left join SC b
on a.S = b.S
group by a.S,a.Sname
order by a.S

--6、查询"李"姓老师的数量
--方法1
select count(Tname) ["李"姓老师的数量] from Teacher where Tname like N‘李%‘
--方法2
select count(Tname) ["李"姓老师的数量] from Teacher where left(Tname,1) = N‘李‘
/*
"李"姓老师的数量
-----------
1
*/

--7、查询学过"张三"老师授课的同学的信息
select distinct Student.* from Student , SC , Course , Teacher
where Student.S = SC.S and SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N‘张三‘
order by Student.S

--8、查询没学过"张三"老师授课的同学的信息
select m.* from Student m where S not in (select distinct SC.S from SC , Course , Teacher where SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N‘张三‘) order by m.S

--9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
--方法1
select Student.* from Student , SC where Student.S = SC.S and SC.C = ‘01‘ and exists (Select 1 from SC SC_2 where SC_2.S = SC.S and SC_2.C = ‘02‘) order by Student.S
--方法2
select Student.* from Student , SC where Student.S = SC.S and SC.C = ‘02‘ and exists (Select 1 from SC SC_2 where SC_2.S = SC.S and SC_2.C = ‘01‘) order by Student.S
--方法3
select m.* from Student m where S in
(
select S from
(
    select distinct S from SC where C = ‘01‘
    union all
    select distinct S from SC where C = ‘02‘
) t group by S having count(1) = 2
)
order by m.S

--10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
--方法1
select Student.* from Student , SC where Student.S = SC.S and SC.C = ‘01‘ and not exists (Select 1 from SC SC_2 where SC_2.S = SC.S and SC_2.C = ‘02‘) order by Student.S
--方法2
select Student.* from Student , SC where Student.S = SC.S and SC.C = ‘01‘ and Student.S not in (Select SC_2.S from SC SC_2 where SC_2.S = SC.S and SC_2.C = ‘02‘) order by Student.S

--11、查询没有学全所有课程的同学的信息
--11.1、
select Student.*
from Student , SC
where Student.S = SC.S
group by Student.S , Student.Sname , Student.Sage , Student.Ssex having count(C) < (select count(C) from Course)
--11.2
select Student.*
from Student left join SC
on Student.S = SC.S
group by Student.S , Student.Sname , Student.Sage , Student.Ssex having count(C) < (select count(C) from Course)

--12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息
select distinct Student.* from Student , SC where Student.S = SC.S and SC.C in (select C from SC where S = ‘01‘) and Student.S <> ‘01‘

--13、查询和"01"号的同学学习的课程完全相同的其他同学的信息
select Student.* from Student where S in
(select distinct SC.S from SC where S <> ‘01‘ and SC.C in (select distinct C from SC where S = ‘01‘)
group by SC.S having count(1) = (select count(1) from SC where S=‘01‘))

--14、查询没学过"张三"老师讲授的任一门课程的学生姓名
select student.* from student where student.S not in
(select distinct sc.S from sc , course , teacher where sc.C = course.C and course.T = teacher.T and teacher.tname = N‘张三‘)
order by student.S

--15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
select student.S , student.sname , cast(avg(score) as decimal(18,2)) avg_score from student , sc
where student.S = SC.S and student.S in (select S from SC where score < 60 group by S having count(1) >= 2)
group by student.S , student.sname

--16、检索"01"课程分数小于60，按分数降序排列的学生信息
select student.* , sc.C , sc.score from student , sc
where student.S = SC.S and sc.score < 60 and sc.C = ‘01‘
order by sc.score desc

--17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
--17.1 SQL 2000 静态
select a.S 学生编号 , a.Sname 学生姓名 ,
       max(case c.Cname when N‘语文‘ then b.score else null end) [语文],
       max(case c.Cname when N‘数学‘ then b.score else null end) [数学],
       max(case c.Cname when N‘英语‘ then b.score else null end) [英语],
       cast(avg(b.score) as decimal(18,2)) 平均分
from Student a
left join SC b on a.S = b.S
left join Course c on b.C = c.C
group by a.S , a.Sname
order by 平均分 desc
--17.2 SQL 2000 动态
declare @sql nvarchar(4000)
set @sql = ‘select a.S ‘ + N‘学生编号‘ + ‘ , a.Sname ‘ + N‘学生姓名‘
select @sql = @sql + ‘,max(case c.Cname when N‘‘‘+Cname+‘‘‘ then b.score else null end) [‘+Cname+‘]‘
from (select distinct Cname from Course) as t
set @sql = @sql + ‘ , cast(avg(b.score) as decimal(18,2)) ‘ + N‘平均分‘ + ‘ from Student a left join SC b on a.S = b.S left join Course c on b.C = c.C
group by a.S , a.Sname order by ‘ + N‘平均分‘ + ‘ desc‘
exec(@sql)
--17.3 有关sql 2005的动静态写法参见我的文章《普通行列转换(version 2.0)》或《普通行列转换(version 3.0)》。

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#1楼得分：0回复于：2010-05-17 17:47:07
SQL code
--18、查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率
--及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
--方法1
select m.C [课程编号], m.Cname [课程名称],
max(n.score) [最高分],
min(n.score) [最低分],
cast(avg(n.score) as decimal(18,2)) [平均分],
cast((select count(1) from SC where C = m.C and score >= 60)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [及格率(%)],
cast((select count(1) from SC where C = m.C and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [中等率(%)],
cast((select count(1) from SC where C = m.C and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [优良率(%)],
cast((select count(1) from SC where C = m.C and score >= 90)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [优秀率(%)]
from Course m , SC n
where m.C = n.C
group by m.C , m.Cname
order by m.C
--方法2
select m.C [课程编号], m.Cname [课程名称],
(select max(score) from SC where C = m.C) [最高分],
(select min(score) from SC where C = m.C) [最低分],
(select cast(avg(score) as decimal(18,2)) from SC where C = m.C) [平均分],
cast((select count(1) from SC where C = m.C and score >= 60)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [及格率(%)],
cast((select count(1) from SC where C = m.C and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [中等率(%)],
cast((select count(1) from SC where C = m.C and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [优良率(%)],
cast((select count(1) from SC where C = m.C and score >= 90)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [优秀率(%)]
from Course m
order by m.C

--19、按各科成绩进行排序，并显示排名
--19.1 sql 2000用子查询完成
--Score重复时保留名次空缺
select t.* , px = (select count(1) from SC where C = t.C and score > t.score) + 1 from sc t order by t.C , px
--Score重复时合并名次
select t.* , px = (select count(distinct score) from SC where C = t.C and score >= t.score) from sc t order by t.C , px
--19.2 sql 2005用rank,DENSE_RANK完成
--Score重复时保留名次空缺(rank完成)
select t.* , px = rank() over(partition by C order by score desc) from sc t order by t.C , px
--Score重复时合并名次(DENSE_RANK完成)
select t.* , px = DENSE_RANK() over(partition by C order by score desc) from sc t order by t.C , px

--20、查询学生的总成绩并进行排名
--20.1 查询学生的总成绩
select m.S [学生编号] ,
       m.Sname [学生姓名] ,
       isnull(sum(score),0) [总成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
order by [总成绩] desc
--20.2 查询学生的总成绩并进行排名，sql 2000用子查询完成，分总分重复时保留名次空缺和不保留名次空缺两种。
select t1.* , px = (select count(1) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(sum(score),0) [总成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t2 where 总成绩 > t1.总成绩) + 1 from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(sum(score),0) [总成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t1
order by px

select t1.* , px = (select count(distinct 总成绩) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(sum(score),0) [总成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t2 where 总成绩 >= t1.总成绩) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(sum(score),0) [总成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t1
order by px
--20.3 查询学生的总成绩并进行排名，sql 2005用rank,DENSE_RANK完成，分总分重复时保留名次空缺和不保留名次空缺两种。
select t.* , px = rank() over(order by [总成绩] desc) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(sum(score),0) [总成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t
order by px

select t.* , px = DENSE_RANK() over(order by [总成绩] desc) from
(
select m.S [学生编号] ,
m.Sname [学生姓名] ,
isnull(sum(score),0) [总成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t
order by px

--21、查询不同老师所教不同课程平均分从高到低显示
select m.T , m.Tname , cast(avg(o.score) as decimal(18,2)) avg_score
from Teacher m , Course n , SC o
where m.T = n.T and n.C = o.C
group by m.T , m.Tname
order by avg_score desc

--22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩
--22.1 sql 2000用子查询完成
--Score重复时保留名次空缺
select * from (select t.* , px = (select count(1) from SC where C = t.C and score > t.score) + 1 from sc t) m where px between 2 and 3 order by m.C , m.px
--Score重复时合并名次
select * from (select t.* , px = (select count(distinct score) from SC where C = t.C and score >= t.score) from sc t) m where px between 2 and 3 order by m.C , m.px
--22.2 sql 2005用rank,DENSE_RANK完成
--Score重复时保留名次空缺(rank完成)
select * from (select t.* , px = rank() over(partition by C order by score desc) from sc t) m where px between 2 and 3 order by m.C , m.px
--Score重复时合并名次(DENSE_RANK完成)
select * from (select t.* , px = DENSE_RANK() over(partition by C order by score desc) from sc t) m where px between 2 and 3 order by m.C , m.px

--23、统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比
--23.1 统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]
--横向显示
select Course.C [课程编号] , Cname as [课程名称] ,
sum(case when score >= 85 then 1 else 0 end) [85-100],
sum(case when score >= 70 and score < 85 then 1 else 0 end) [70-85],
sum(case when score >= 60 and score < 70 then 1 else 0 end) [60-70],
sum(case when score < 60 then 1 else 0 end) [0-60]
from sc , Course
where SC.C = Course.C
group by Course.C , Course.Cname
order by Course.C
--纵向显示1(显示存在的分数段)
select m.C [课程编号] , m.Cname [课程名称] , 分数段 = (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end) ,
count(1) 数量
from Course m , sc n
where m.C = n.C
group by m.C , m.Cname , (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end)
order by m.C , m.Cname , 分数段
--纵向显示2(显示存在的分数段，不存在的分数段用0显示)
select m.C [课程编号] , m.Cname [课程名称] , 分数段 = (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end) ,
count(1) 数量
from Course m , sc n
where m.C = n.C
group by all m.C , m.Cname , (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end)
order by m.C , m.Cname , 分数段

--23.2 统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[<60]及所占百分比
--横向显示
select m.C 课程编号, m.Cname 课程名称,
(select count(1) from SC where C = m.C and score < 60) [0-60],
cast((select count(1) from SC where C = m.C and score < 60)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [百分比(%)],
(select count(1) from SC where C = m.C and score >= 60 and score < 70) [60-70],
cast((select count(1) from SC where C = m.C and score >= 60 and score < 70)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [百分比(%)],
(select count(1) from SC where C = m.C and score >= 70 and score < 85) [70-85],
cast((select count(1) from SC where C = m.C and score >= 70 and score < 85)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [百分比(%)],
(select count(1) from SC where C = m.C and score >= 85) [85-100],
cast((select count(1) from SC where C = m.C and score >= 85)*100.0 / (select count(1) from SC where C = m.C) as decimal(18,2)) [百分比(%)]
from Course m
order by m.C
--纵向显示1(显示存在的分数段)
select m.C [课程编号] , m.Cname [课程名称] , 分数段 = (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end) ,
count(1) 数量 ,
cast(count(1) * 100.0 / (select count(1) from sc where C = m.C) as decimal(18,2)) [百分比(%)]
from Course m , sc n
where m.C = n.C
group by m.C , m.Cname , (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end)
order by m.C , m.Cname , 分数段
--纵向显示2(显示存在的分数段，不存在的分数段用0显示)
select m.C [课程编号] , m.Cname [课程名称] , 分数段 = (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end) ,
count(1) 数量 ,
cast(count(1) * 100.0 / (select count(1) from sc where C = m.C) as decimal(18,2)) [百分比(%)]
from Course m , sc n
where m.C = n.C
group by all m.C , m.Cname , (
case when n.score >= 85 then ‘85-100‘
       when n.score >= 70 and n.score < 85 then ‘70-85‘
       when n.score >= 60 and n.score < 70 then ‘60-70‘
       else ‘0-60‘
end)
order by m.C , m.Cname , 分数段

对我有用[6]丢个板砖[0]引用举报管理TOP
精华推荐：SQL语句优化汇总

dawugui
(爱新觉罗.毓华)
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#2楼得分：0回复于：2010-05-17 17:47:22
SQL code
--24、查询学生平均成绩及其名次
--24.1 查询学生的平均成绩并进行排名，sql 2000用子查询完成，分平均成绩重复时保留名次空缺和不保留名次空缺两种。
select t1.* , px = (select count(1) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(cast(avg(score) as decimal(18,2)),0) [平均成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t2 where 平均成绩 > t1.平均成绩) + 1 from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(cast(avg(score) as decimal(18,2)),0) [平均成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t1
order by px

select t1.* , px = (select count(distinct 平均成绩) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(cast(avg(score) as decimal(18,2)),0) [平均成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t2 where 平均成绩 >= t1.平均成绩) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(cast(avg(score) as decimal(18,2)),0) [平均成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t1
order by px
--24.2 查询学生的平均成绩并进行排名，sql 2005用rank,DENSE_RANK完成，分平均成绩重复时保留名次空缺和不保留名次空缺两种。
select t.* , px = rank() over(order by [平均成绩] desc) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(cast(avg(score) as decimal(18,2)),0) [平均成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t
order by px

select t.* , px = DENSE_RANK() over(order by [平均成绩] desc) from
(
select m.S [学生编号] ,
         m.Sname [学生姓名] ,
         isnull(cast(avg(score) as decimal(18,2)),0) [平均成绩]
from Student m left join SC n on m.S = n.S
group by m.S , m.Sname
) t
order by px

--25、查询各科成绩前三名的记录
--25.1 分数重复时保留名次空缺
select m.* , n.C , n.score from Student m, SC n where m.S = n.S and n.score in
(select top 3 score from sc where C = n.C order by score desc) order by n.C , n.score desc
--25.2 分数重复时不保留名次空缺，合并名次
--sql 2000用子查询实现
select * from (select t.* , px = (select count(distinct score) from SC where C = t.C and score >= t.score) from sc t) m where px between 1 and 3 order by m.C , m.px
--sql 2005用DENSE_RANK实现
select * from (select t.* , px = DENSE_RANK() over(partition by C order by score desc) from sc t) m where px between 1 and 3 order by m.C , m.px

--26、查询每门课程被选修的学生数
select C , count(S)[学生数] from sc group by C

--27、查询出只有两门课程的全部学生的学号和姓名
select Student.S , Student.Sname
from Student , SC
where Student.S = SC.S
group by Student.S , Student.Sname
having count(SC.C) = 2
order by Student.S

--28、查询男生、女生人数
select count(Ssex) as 男生人数 from Student where Ssex = N‘男‘
select count(Ssex) as 女生人数 from Student where Ssex = N‘女‘
select sum(case when Ssex = N‘男‘ then 1 else 0 end) [男生人数],sum(case when Ssex = N‘女‘ then 1 else 0 end) [女生人数] from student
select case when Ssex = N‘男‘ then N‘男生人数‘ else N‘女生人数‘ end [男女情况] , count(1) [人数] from student group by case when Ssex = N‘男‘ then N‘男生人数‘ else N‘女生人数‘ end

--29、查询名字中含有"风"字的学生信息
select * from student where sname like N‘%风%‘
select * from student where charindex(N‘风‘ , sname) > 0

--30、查询同名同性学生名单，并统计同名人数
select Sname [学生姓名], count(*) [人数] from Student group by Sname having count(*) > 1

--31、查询1990年出生的学生名单(注：Student表中Sage列的类型是datetime)
select * from Student where year(sage) = 1990
select * from Student where datediff(yy,sage,‘1990-01-01‘) = 0
select * from Student where datepart(yy,sage) = 1990
select * from Student where convert(varchar(4),sage,120) = ‘1990‘

--32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列
select m.C , m.Cname , cast(avg(n.score) as decimal(18,2)) avg_score
from Course m, SC n
where m.C = n.C
group by m.C , m.Cname
order by avg_score desc, m.C asc

--33、查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩
select a.S , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score
from Student a , sc b
where a.S = b.S
group by a.S , a.Sname
having cast(avg(b.score) as decimal(18,2)) >= 85
order by a.S

--34、查询课程名称为"数学"，且分数低于60的学生姓名和分数
select sname , score
from Student , SC , Course
where SC.S = Student.S and SC.C = Course.C and Course.Cname = N‘数学‘ and score < 60

--35、查询所有学生的课程及分数情况；
select Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course
where Student.S = SC.S and SC.C = Course.C
order by Student.S , SC.C

--36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数；
select Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course
where Student.S = SC.S and SC.C = Course.C and SC.score >= 70
order by Student.S , SC.C

--37、查询不及格的课程
select Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course
where Student.S = SC.S and SC.C = Course.C and SC.score < 60
order by Student.S , SC.C

--38、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名；
select Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course
where Student.S = SC.S and SC.C = Course.C and SC.C = ‘01‘ and SC.score >= 80
order by Student.S , SC.C

--39、求每门课程的学生人数
select Course.C , Course.Cname , count(*) [学生人数]
from Course , SC
where Course.C = SC.C
group by Course.C , Course.Cname
order by Course.C , Course.Cname

--40、查询选修"张三"老师所授课程的学生中，成绩最高的学生信息及其成绩
--40.1 当最高分只有一个时
select top 1 Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course , Teacher
where Student.S = SC.S and SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N‘张三‘
order by SC.score desc
--40.2 当最高分出现多个时
select Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course , Teacher
where Student.S = SC.S and SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N‘张三‘ and
SC.score = (select max(SC.score) from SC , Course , Teacher where SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N‘张三‘)

--41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩
--方法1
select m.* from SC m ,(select C , score from SC group by C , score having count(1) > 1) n
where m.C= n.C and m.score = n.score order by m.C , m.score , m.S
--方法2
select m.* from SC m where exists (select 1 from (select C , score from SC group by C , score having count(1) > 1) n
where m.C= n.C and m.score = n.score) order by m.C , m.score , m.S

--42、查询每门功成绩最好的前两名
select t.* from sc t where score in (select top 2 score from sc where C = T.C order by score desc) order by t.C , t.score desc

--43、统计每门课程的学生选修人数（超过5人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列
select Course.C , Course.Cname , count(*) [学生人数]
from Course , SC
where Course.C = SC.C
group by Course.C , Course.Cname
having count(*) >= 5
order by [学生人数] desc , Course.C

--44、检索至少选修两门课程的学生学号
select student.S , student.Sname
from student , SC
where student.S = SC.S
group by student.S , student.Sname
having count(1) >= 2
order by student.S

--45、查询选修了全部课程的学生信息
--方法1 根据数量来完成
select student.* from student where S in
(select S from sc group by S having count(1) = (select count(1) from course))
--方法2 使用双重否定来完成
select t.* from student t where t.S not in
(
select distinct m.S from
(
select S , C from student , course
) m where not exists (select 1 from sc n where n.S = m.S and n.C = m.C)
)
--方法3 使用双重否定来完成
select t.* from student t where not exists(select 1 from
(
select distinct m.S from
(
select S , C from student , course
) m where not exists (select 1 from sc n where n.S = m.S and n.C = m.C)
) k where k.S = t.S
)

--46、查询各学生的年龄
--46.1 只按照年份来算
select * , datediff(yy , sage , getdate()) [年龄] from student
--46.2 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一
select * , case when right(convert(varchar(10),getdate(),120),5) < right(convert(varchar(10),sage,120),5) then datediff(yy , sage , getdate()) - 1 else datediff(yy , sage , getdate()) end [年龄] from student

--47、查询本周过生日的学生
select * from student where datediff(week,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = 0

--48、查询下周过生日的学生
select * from student where datediff(week,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = -1

--49、查询本月过生日的学生
select * from student where datediff(mm,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = 0

--50、查询下月过生日的学生
select * from student where datediff(mm,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = -1

drop table Student,Course,Teacher,SC

--1.学生表
Student(S,Sname,Sage,Ssex) --S 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别
--2.课程表
Course(C,Cname,T) --C --课程编号,Cname 课程名称,T 教师编号
--3.教师表
Teacher(T,Tname) --T 教师编号,Tname 教师姓名
--4.成绩表
SC(S,C,score) --S 学生编号,C 课程编号,score 分数
*/
--创建测试数据
create table Student(S varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10))
insert into Student values(‘01‘ , N‘赵雷‘ , ‘1990-01-01‘ , N‘男‘)
insert into Student values(‘02‘ , N‘钱电‘ , ‘1990-12-21‘ , N‘男‘)
insert into Student values(‘03‘ , N‘孙风‘ , ‘1990-05-20‘ , N‘男‘)
insert into Student values(‘04‘ , N‘李云‘ , ‘1990-08-06‘ , N‘男‘)
insert into Student values(‘05‘ , N‘周梅‘ , ‘1991-12-01‘ , N‘女‘)
insert into Student values(‘06‘ , N‘吴兰‘ , ‘1992-03-01‘ , N‘女‘)
insert into Student values(‘07‘ , N‘郑竹‘ , ‘1989-07-01‘ , N‘女‘)
insert into Student values(‘08‘ , N‘王菊‘ , ‘1990-01-20‘ , N‘女‘)
create table Course(C varchar(10),Cname nvarchar(10),T varchar(10))
insert into Course values(‘01‘ , N‘语文‘ , ‘02‘)
insert into Course values(‘02‘ , N‘数学‘ , ‘01‘)
insert into Course values(‘03‘ , N‘英语‘ , ‘03‘)
create table Teacher(T varchar(10),Tname nvarchar(10))
insert into Teacher values(‘01‘ , N‘张三‘)
insert into Teacher values(‘02‘ , N‘李四‘)
insert into Teacher values(‘03‘ , N‘王五‘)
create table SC(S varchar(10),C varchar(10),score decimal(18,1))
insert into SC values(‘01‘ , ‘01‘ , 80)
insert into SC values(‘01‘ , ‘02‘ , 90)
insert into SC values(‘01‘ , ‘03‘ , 99)
insert into SC values(‘02‘ , ‘01‘ , 70)
insert into SC values(‘02‘ , ‘02‘ , 60)
insert into SC values(‘02‘ , ‘03‘ , 80)
insert into SC values(‘03‘ , ‘01‘ , 80)
insert into SC values(‘03‘ , ‘02‘ , 80)
insert into SC values(‘03‘ , ‘03‘ , 80)
insert into SC values(‘04‘ , ‘01‘ , 50)
insert into SC values(‘04‘ , ‘02‘ , 30)
insert into SC values(‘04‘ , ‘03‘ , 20)
insert into SC values(‘05‘ , ‘01‘ , 76)
insert into SC values(‘05‘ , ‘02‘ , 87)
insert into SC values(‘06‘ , ‘01‘ , 31)
insert into SC values(‘06‘ , ‘03‘ , 34)
insert into SC values(‘07‘ , ‘02‘ , 89)
insert into SC values(‘07‘ , ‘03‘ , 98)
go

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--26、查询每门课程被选修的学生数
select C , count(S)[学生数] from sc group by C

--29、查询名字中含有"风"字的学生信息
select * from student where sname like N‘%风%‘
select * from student where charindex(N‘风‘ , sname) > 0

--35、查询所有学生的课程及分数情况；
select Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course
where Student.S = SC.S and SC.C = Course.C
order by Student.S , SC.C

--37、查询不及格的课程
select Student.* , Course.Cname , SC.C , SC.score
from Student, SC , Course
where Student.S = SC.S and SC.C = Course.C and SC.score < 60
order by Student.S , SC.C

--39、求每门课程的学生人数
select Course.C , Course.Cname , count(*) [学生人数]
from Course , SC
where Course.C = SC.C
group by Course.C , Course.Cname
order by Course.C , Course.Cname