--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\'
--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)》。
--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
--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
-- 建表
-- 学生表
CREATE TABLE `Student`(
`s_id` VARCHAR(20),
`s_name` VARCHAR(20) NOT NULL DEFAULT \'\',
`s_birth` VARCHAR(20) NOT NULL DEFAULT \'\',
`s_sex` VARCHAR(10) NOT NULL DEFAULT \'\',
PRIMARY KEY(`s_id`)
);
-- 课程表
CREATE TABLE `Course`(
`c_id` VARCHAR(20),
`c_name` VARCHAR(20) NOT NULL DEFAULT \'\',
`t_id` VARCHAR(20) NOT NULL,
PRIMARY KEY(`c_id`)
);
-- 教师表
CREATE TABLE `Teacher`(
`t_id` VARCHAR(20),
`t_name` VARCHAR(20) NOT NULL DEFAULT \'\',
PRIMARY KEY(`t_id`)
);
-- 成绩表
CREATE TABLE `Score`(
`s_id` VARCHAR(20),
`c_id` VARCHAR(20),
`s_score` INT(3),
PRIMARY KEY(`s_id`,`c_id`)
);
-- 插入学生表测试数据
insert into Student values(\'01\' , \'赵雷\' , \'1990-01-01\' , \'男\');
insert into Student values(\'02\' , \'钱电\' , \'1990-12-21\' , \'男\');
insert into Student values(\'03\' , \'孙风\' , \'1990-05-20\' , \'男\');
insert into Student values(\'04\' , \'李云\' , \'1990-08-06\' , \'男\');
insert into Student values(\'05\' , \'周梅\' , \'1991-12-01\' , \'女\');
insert into Student values(\'06\' , \'吴兰\' , \'1992-03-01\' , \'女\');
insert into Student values(\'07\' , \'郑竹\' , \'1989-07-01\' , \'女\');
insert into Student values(\'08\' , \'王菊\' , \'1990-01-20\' , \'女\');
-- 课程表测试数据
insert into Course values(\'01\' , \'语文\' , \'02\');
insert into Course values(\'02\' , \'数学\' , \'01\');
insert into Course values(\'03\' , \'英语\' , \'03\');
-- 教师表测试数据
insert into Teacher values(\'01\' , \'张三\');
insert into Teacher values(\'02\' , \'李四\');
insert into Teacher values(\'03\' , \'王五\');
-- 成绩表测试数据
insert into Score values(\'01\' , \'01\' , 80);
insert into Score values(\'01\' , \'02\' , 90);
insert into Score values(\'01\' , \'03\' , 99);
insert into Score values(\'02\' , \'01\' , 70);
insert into Score values(\'02\' , \'02\' , 60);
insert into Score values(\'02\' , \'03\' , 80);
insert into Score values(\'03\' , \'01\' , 80);
insert into Score values(\'03\' , \'02\' , 80);
insert into Score values(\'03\' , \'03\' , 80);
insert into Score values(\'04\' , \'01\' , 50);
insert into Score values(\'04\' , \'02\' , 30);
insert into Score values(\'04\' , \'03\' , 20);
insert into Score values(\'05\' , \'01\' , 76);
insert into Score values(\'05\' , \'02\' , 87);
insert into Score values(\'06\' , \'01\' , 31);
insert into Score values(\'06\' , \'03\' , 34);
insert into Score values(\'07\' , \'02\' , 89);
insert into Score values(\'07\' , \'03\' , 98);
/*
-- 准备条件,去掉 sql_mode 的 ONLY_FULL_GROUP_BY 否则此种情况下会报错:
-- Expression #1 of select list is not in group by clause and contains nonaggregated column \'userinfo.
-- 原因：
-- MySQL 5.7.5和up实现了对功能依赖的检测。如果启用了only_full_group_by SQL模式(在默认情况下是这样)，
-- 那么MySQL就会拒绝选择列表、条件或顺序列表引用的查询，这些查询将引用组中未命名的非聚合列，而不是在功能上依赖于它们。
-- (在5.7.5之前，MySQL没有检测到功能依赖项，only_full_group_by在默认情况下是不启用的。关于前5.7.5行为的描述，请参阅MySQL 5.6参考手册。)
-- 执行以下个命令，可以查看 sql_mode 的内容。
SHOW SESSION VARIABLES;
SHOW GLOBAL VARIABLES;
select @@sql_mode;
-- 更改
set global sql_mode=\'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION\';
set session sql_mode=\'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION\';
*/
-- 1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
select st.*,sc.s_score as \'语文\' ,sc2.s_score \'数学\'
from student st
left join score sc on sc.s_id=st.s_id and sc.c_id=\'01\'
left join score sc2 on sc2.s_id=st.s_id and sc2.c_id=\'02\'
where sc.s_score>sc2.s_score
-- 2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
select st.*,sc.s_score \'语文\',sc2.s_score \'数学\' from student st
left join score sc on sc.s_id=st.s_id and sc.c_id=\'01\'
left join score sc2 on sc2.s_id=st.s_id and sc2.c_id=\'02\'
where sc.s_score<sc2.s_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 st.s_id,st.s_name,ROUND(AVG(sc.s_score),2) "平均成绩" from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id having AVG(sc.s_score)>=60
-- 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
-- (包括有成绩的和无成绩的)
select st.s_id,st.s_name,(case when ROUND(AVG(sc.s_score),2) is null then 0 else ROUND(AVG(sc.s_score),2) end ) "平均成绩" from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id having AVG(sc.s_score)<60 or AVG(sc.s_score) is NULL
-- 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
select st.s_id,st.s_name,count(sc.c_id) "选课总数",sum(case when sc.s_score is null then 0 else sc.s_score end) "总成绩" from student st left join score sc on st.s_id = sc.s_id group by st.s_id
-- 6、查询"李"姓老师的数量
select t.t_name,count(t.t_id) from teacher t
group by t.t_id having t.t_name like "李%";
-- 7、查询学过"张三"老师授课的同学的信息
select st.* from student st
left join score sc on sc.s_id=st.s_id
left join course c on c.c_id=sc.c_id
left join teacher t on t.t_id=c.t_id
where t.t_name="张三"
-- 8、查询没学过"张三"老师授课的同学的信息
-- 张三老师教的课
select c.* from course c left join teacher t on t.t_id=c.t_id where t.t_name="张三"
-- 有张三老师课成绩的st.s_id
select sc.s_id from score sc where sc.c_id in (select c.c_id from course c left join teacher t on t.t_id=c.t_id where t.t_name="张三")
-- 不在上面查到的st.s_id的学生信息,即没学过张三老师授课的同学信息
select st.* from student st where st.s_id not in(
select sc.s_id from score sc where sc.c_id in (select c.c_id from course c left join teacher t on t.t_id=c.t_id where t.t_name="张三")
)
-- 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
select st.* from student st
inner join score sc on sc.s_id = st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id="01"
where st.s_id in (
select st2.s_id from student st2
inner join score sc2 on sc2.s_id = st2.s_id
inner join course c2 on c2.c_id=sc2.c_id and c2.c_id="02"
)
select a.* from student a, score b, score c
where a.s_id = b.s_id and a.s_id = c.s_id and b.c_id = \'01\' and c.c_id = \'02\';
-- 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
select st.* from student st
inner join score sc on sc.s_id = st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id="01"
where st.s_id not in (
select st2.s_id from student st2
inner join score sc2 on sc2.s_id = st2.s_id
inner join course c2 on c2.c_id=sc2.c_id and c2.c_id="02"
)
-- 11、查询没有学全所有课程的同学的信息
select * from student where s_id not in (
select st.s_id from student st
inner join score sc on sc.s_id = st.s_id and sc.c_id="01"
where st.s_id in (
select st1.s_id from student st1
inner join score sc2 on sc2.s_id = st1.s_id and sc2.c_id="02"
) and st.s_id in (
select st2.s_id from student st2
inner join score sc2 on sc2.s_id = st2.s_id and sc2.c_id="03"
))
select a.*
from student a
left join score b on a.s_id = b.s_id
group by
a.s_id
having
count(b.c_id) != \'3\';
-- 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 st.* from student st
left join score sc on sc.s_id=st.s_id
where sc.c_id in (
select sc2.c_id from student st2
left join score sc2 on sc2.s_id=st2.s_id
where st2.s_id =\'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 st.* from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id
having group_concat(sc.c_id) =
(
select group_concat(sc2.c_id) from student st2
left join score sc2 on sc2.s_id=st2.s_id
where st2.s_id =\'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 st.s_name from student st
where st.s_id not in (
select sc.s_id from score sc
inner join course c on c.c_id=sc.c_id
inner join teacher t on t.t_id=c.t_id and t.t_name="张三"
)
-- 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 st.s_id,st.s_name,avg(sc.s_score) from student st
left join score sc on sc.s_id=st.s_id
where sc.s_id in (
select sc.s_id from score sc
where sc.s_score<60 or sc.s_score is NULL
group by sc.s_id having COUNT(1)>=2
)
group by st.s_id
-- 16、检索"01"课程分数小于60，按分数降序排列的学生信息
select st.*,sc.s_score from student st
inner join score sc on sc.s_id=st.s_id and sc.c_id="01" and sc.s_score<60
order by sc.s_score desc
select st.*,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
where sc.c_id="01" and sc.s_score<60
order by sc.s_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
select st.s_id,st.s_name,avg(sc4.s_score) "平均分",sc.s_score "语文",sc2.s_score "数学",sc3.s_score "英语" from student st
left join score sc on sc.s_id=st.s_id and sc.c_id="01"
left join score sc2 on sc2.s_id=st.s_id and sc2.c_id="02"
left join score sc3 on sc3.s_id=st.s_id and sc3.c_id="03"
left join score sc4 on sc4.s_id=st.s_id
group by st.s_id
order by avg(sc4.s_score) desc
select st.s_id,st.s_name,
(case when avg(sc4.s_score) is null then 0 else avg(sc4.s_score) end) "平均分",
(case when sc.s_score is null then 0 else sc.s_score end) "语文",
(case when sc2.s_score is null then 0 else sc2.s_score end) "数学",
(case when sc3.s_score is null then 0 else sc3.s_score end) "英语"
from student st
left join score sc on sc.s_id=st.s_id and sc.c_id="01"
left join score sc2 on sc2.s_id=st.s_id and sc2.c_id="02"
left join score sc3 on sc3.s_id=st.s_id and sc3.c_id="03"
left join score sc4 on sc4.s_id=st.s_id
group by st.s_id
order by avg(sc4.s_score) desc
-- 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
select c.c_id,c.c_name,max(sc.s_score) "最高分",MIN(sc2.s_score) "最低分",avg(sc3.s_score) "平均分"
,((select count(s_id) from score where s_score>=60 and c_id=c.c_id )/(select count(s_id) from score where c_id=c.c_id)) "及格率"
,((select count(s_id) from score where s_score>=70 and s_score<80 and c_id=c.c_id )/(select count(s_id) from score where c_id=c.c_id)) "中等率"
,((select count(s_id) from score where s_score>=80 and s_score<90 and c_id=c.c_id )/(select count(s_id) from score where c_id=c.c_id)) "优良率"
,((select count(s_id) from score where s_score>=90 and c_id=c.c_id )/(select count(s_id) from score where c_id=c.c_id)) "优秀率"
from course c
left join score sc on sc.c_id=c.c_id
left join score sc2 on sc2.c_id=c.c_id
left join score sc3 on sc3.c_id=c.c_id
group by c.c_id
-- 19、按各科成绩进行排序，并显示排名(实现不完全)
-- mysql没有rank函数
-- 加@score是为了防止用union all 后打乱了顺序
select c1.s_id,c1.c_id,c1.c_name,@score:=c1.s_score,@i:=@i+1 from (select c.c_name,sc.* from course c
left join score sc on sc.c_id=c.c_id
where c.c_id="01" order by sc.s_score desc) c1 ,
(select @i:=0) a
union all
select c2.s_id,c2.c_id,c2.c_name,c2.s_score,@ii:=@ii+1 from (select c.c_name,sc.* from course c
left join score sc on sc.c_id=c.c_id
where c.c_id="02" order by sc.s_score desc) c2 ,
(select @ii:=0) aa
union all
select c3.s_id,c3.c_id,c3.c_name,c3.s_score,@iii:=@iii+1 from (select c.c_name,sc.* from course c
left join score sc on sc.c_id=c.c_id
where c.c_id="03" order by sc.s_score desc) c3;
set @iii=0;
-- 20、查询学生的总成绩并进行排名
select st.s_id,st.s_name
,(case when sum(sc.s_score) is null then 0 else sum(sc.s_score) end)
from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id order by sum(sc.s_score) desc
-- 21、查询不同老师所教不同课程平均分从高到低显示
select t.t_id,t.t_name,c.c_name,avg(sc.s_score) from teacher t
left join course c on c.t_id=t.t_id
left join score sc on sc.c_id =c.c_id
group by t.t_id
order by avg(sc.s_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
select a.* from (
select st.*,c.c_id,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id =sc.c_id and c.c_id="01"
order by sc.s_score desc LIMIT 1,2 ) a
union all
select b.* from (
select st.*,c.c_id,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id =sc.c_id and c.c_id="02"
order by sc.s_score desc LIMIT 1,2) b
union all
select c.* from (
select st.*,c.c_id,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id =sc.c_id and c.c_id="03"
order by sc.s_score desc LIMIT 1,2) c
-- 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
select c.c_id,c.c_name
,((select count(1) from score sc where sc.c_id=c.c_id and sc.s_score<=100 and sc.s_score>80)/(select count(1) from score sc where sc.c_id=c.c_id )) "100-85"
,((select count(1) from score sc where sc.c_id=c.c_id and sc.s_score<=85 and sc.s_score>70)/(select count(1) from score sc where sc.c_id=c.c_id )) "85-70"
,((select count(1) from score sc where sc.c_id=c.c_id and sc.s_score<=70 and sc.s_score>60)/(select count(1) from score sc where sc.c_id=c.c_id )) "70-60"
,((select count(1) from score sc where sc.c_id=c.c_id and sc.s_score<=60 and sc.s_score>=0)/(select count(1) from score sc where sc.c_id=c.c_id )) "60-0"
from course c order by c.c_id
-- 24、查询学生平均成绩及其名次
set @i=0;
select a.*,@i:=@i+1 from (
select st.s_id,st.s_name,round((case when avg(sc.s_score) is null then 0 else avg(sc.s_score) end),2) "平均分" from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id order by sc.s_score desc) a
-- 25、查询各科成绩前三名的记录
select a.* from (
select st.s_id,st.s_name,c.c_id,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id=\'01\'
order by sc.s_score desc LIMIT 0,3) a
union all
select b.* from (
select st.s_id,st.s_name,c.c_id,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id=\'02\'
order by sc.s_score desc LIMIT 0,3) b
union all
select c.* from (
select st.s_id,st.s_name,c.c_id,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id=\'03\'
order by sc.s_score desc LIMIT 0,3) c
-- 26、查询每门课程被选修的学生数
select c.c_id,c.c_name,count(1) from course c
left join score sc on sc.c_id=c.c_id
inner join student st on st.s_id=c.c_id
group by st.s_id
-- 27、查询出只有两门课程的全部学生的学号和姓名
select st.s_id,st.s_name from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id
group by st.s_id having count(1)=2
-- 28、查询男生、女生人数
select st.s_sex,count(1) from student st group by st.s_sex
-- 29、查询名字中含有"风"字的学生信息
select st.* from student st where st.s_name like "%风%";
-- 30、查询同名同性学生名单，并统计同名人数
select st.*,count(1) from student st group by st.s_name,st.s_sex having count(1)>1
-- 31、查询1990年出生的学生名单
select st.* from student st where st.s_birth like "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 c.c_id,c.c_name,avg(sc.s_score) from course c
inner join score sc on sc.c_id=c.c_id
group by c.c_id order by avg(sc.s_score) desc,c.c_id 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 st.s_id,st.s_name,avg(sc.s_score) from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id having avg(sc.s_score)>=85
-- 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 st.s_id,st.s_name,sc.s_score from student st
inner join score sc on sc.s_id=st.s_id and sc.s_score<60
inner join course c on c.c_id=sc.c_id and c.c_name ="数学"
-- 35、查询所有学生的课程及分数情况；
select st.s_id,st.s_name,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
left join course c on c.c_id =sc.c_id
order by st.s_id,c.c_name
-- 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 st2.s_id,st2.s_name,c2.c_name,sc2.s_score from student st2
left join score sc2 on sc2.s_id=st2.s_id
left join course c2 on c2.c_id=sc2.c_id
where st2.s_id in(
select st.s_id from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id having min(sc.s_score)>=70)
order by s_id
-- 37、查询不及格的课程
select st.s_id,c.c_name,st.s_name,sc.s_score from student st
inner join score sc on sc.s_id=st.s_id and sc.s_score<60
inner join course c on c.c_id=sc.c_id
-- 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 st.s_id,st.s_name,sc.s_score from student st
inner join score sc on sc.s_id=st.s_id and sc.c_id="01" and sc.s_score>=80
-- 39、求每门课程的学生人数
select c.c_id,c.c_name,count(1) from course c
inner join score sc on sc.c_id=c.c_id
group by c.c_id
-- 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
select st.*,c.c_name,sc.s_score,t.t_name from student st
inner join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id
inner join teacher t on t.t_id=c.t_id and t.t_name="张三"
order by sc.s_score desc
limit 0,1
-- 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
select st.s_id,st.s_name,sc.c_id,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
left join course c on c.c_id=sc.c_id
where (
select count(1) from student st2
left join score sc2 on sc2.s_id=st2.s_id
left join course c2 on c2.c_id=sc2.c_id
where sc.s_score=sc2.s_score and c.c_id!=c2.c_id
)>1
-- 42、查询每门功成绩最好的前两名
select a.* from (select st.s_id,st.s_name,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id="01"
order by sc.s_score desc limit 0,2) a
union all
select b.* from (select st.s_id,st.s_name,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id="02"
order by sc.s_score desc limit 0,2) b
union all
select c.* from (select st.s_id,st.s_name,c.c_name,sc.s_score from student st
left join score sc on sc.s_id=st.s_id
inner join course c on c.c_id=sc.c_id and c.c_id="03"
order by sc.s_score desc limit 0,2) c
-- 借鉴(更准确,漂亮):
select a.s_id,a.c_id,a.s_score from score a
where (select COUNT(1) from score b where b.c_id=a.c_id and b.s_score>=a.s_score)<=2 order by a.c_id
-- 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 sc.c_id,count(1) from score sc
left join course c on c.c_id=sc.c_id
group by c.c_id having count(1)>5
order by count(1) desc,sc.c_id asc
-- 44、检索至少选修两门课程的学生学号
select st.s_id from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id having count(1)>=2
-- 45、查询选修了全部课程的学生信息
select st.* from student st
left join score sc on sc.s_id=st.s_id
group by st.s_id having count(1)=(select count(1) from course)
-- 46、查询各学生的年龄
select st.*,timestampdiff(year,st.s_birth,now()) from student st
-- 47、查询本周过生日的学生
-- 此处可能有问题,week函数取的为当前年的第几周,2017-12-12是第50周而2018-12-12是第49周,可以取月份,day,星期几(%w),
-- 再判断本周是否会持续到下一个月进行判断,太麻烦,不会写
select st.* from student st
where week(now())=week(date_format(st.s_birth,\'%Y%m%d\'))
-- 48、查询下周过生日的学生
select st.* from student st
where week(now())+1=week(date_format(st.s_birth,\'%Y%m%d\'))
-- 49、查询本月过生日的学生
select st.* from student st
where month(now())=month(date_format(st.s_birth,\'%Y%m%d\'))
-- 50、查询下月过生日的学生
-- 注意:当 当前月为12时,用month(now())+1为13而不是1,可用timestampadd()函数或mod取模
select st.* from student st
where month(timestampadd(month,1,now()))=month(date_format(st.s_birth,\'%Y%m%d\'))
-- 或
select st.* from student st where (month(now()) + 1) mod 12 = month(date_format(st.s_birth,\'%Y%m%d\'))