50个经典SQL语句

一、SQL Server版

--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

二、MySQL版

-- 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),
`grade` 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);

-- 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.grade '语文' ,sc2.grade '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.grade>sc2.grade

-- 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.grade '语文',sc2.grade '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.grade<sc2.grade

-- 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.grade),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.grade)>=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.grade),2) is null then 0 else ROUND(AVG(sc.grade),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.grade)<60 or AVG(sc.grade) 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.grade is null then 0 else sc.grade 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 
join Score sc on sc.s_id=st.s_id
join Course c on c.c_id=sc.c_id
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 join Teacher t on t.t_name="张三" and t.t_id=c.t_id
-- 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 join Teacher t on t.t_id=c.t_id where  t.t_name="张三")
-- 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 join Course c on sc.c_id=c.c_id join Teacher t on t.t_id=c.t_id and 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
-- 方法1:
select  st.* from Student st 
inner join Score sc on sc.s_id = st.s_id and (sc.c_id in ("01","02"))
group by st.s_id having count(1)=2;
-- 方法2:
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 
join Score sc on sc.s_id = st.s_id and sc.c_id="01"
where st.s_id not in (
select st2.s_id from Student st2 join Score sc2 on sc2.s_id = st2.s_id and sc2.c_id="02"
);

-- 11、查询没有学全所有课程的同学的信息
select a.* from Student a left join Score b on a.s_id = b.s_id group by a.s_id having count(1) != 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 join Score sc on sc.s_id=st.s_id join (
select c_id from Student a join Score b on b.s_id=a.s_id where a.s_id ='01'
) t on t.c_id=sc.c_id

-- 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 join Score sc on sc.s_id=st.s_id
group by st.s_id having group_concat(sc.c_id) = 
(select group_concat(b.c_id) from Student a join Score b on a.s_id=b.s_id where a.s_id ='01' order by b.s_id)
order by sc.c_id;

-- 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 join Course c on c.c_id=sc.c_id 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.grade) from Student st
join Score sc on sc.s_id=st.s_id 
where ifnull(sc.grade,0)<60
group by st.s_id having count(1)>=2;

-- 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.grade from Student st 
join Score sc on sc.s_id=st.s_id and sc.c_id="01" and sc.grade<60
order by sc.grade 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.grade) "平均分",sc.grade "语文",sc2.grade "数学",sc3.grade "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.grade) desc

select st.s_id,st.s_name,
(case when avg(sc4.grade) is null then 0 else avg(sc4.grade) end) "平均分",
(case when sc.grade is null then 0 else sc.grade end) "语文",
(case when sc2.grade is null then 0 else sc2.grade end) "数学",
(case when sc3.grade is null then 0 else sc3.grade 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.grade) 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 课程ID,c.c_name 课程,max(sc.grade) 最高分,MIN(sc.grade) 最低分,avg(sc.grade) 平均分 
,sum(case when sc.grade>=60 then 1 else 0 end)/(count(1)) 及格率
,sum(case when sc.grade>=70 and sc.grade<80 then 1 else 0 end)/(count(1)) 中等率
,sum(case when sc.grade>=80 and sc.grade<90 then 1 else 0 end)/(count(1)) 优良率
,sum(case when sc.grade>=90 then 1 else 0 end)/(count(1)) 优秀率
from Course c
join Score sc on sc.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
select sc.s_id 学生ID,c.c_name 课程,sc.grade 成绩,rank()over(partition by sc.c_id order by sc.grade desc) as 排名 
from Score sc join Course c on sc.c_id=c.c_id;

-- 20、查询学生的总成绩并进行排名
select *,rank()over(order by 总成绩 desc) 排名
from (select st.s_id,st.s_name 学生,(case when sum(sc.grade) is null then 0 else sum(sc.grade) end) 总成绩
from Student st left join Score sc on sc.s_id=st.s_id group by st.s_id)t;

-- 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 老师,c.c_name 课程,avg(sc.grade) 平均分 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.grade) 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 * from (
  select s.*,c.c_name,sc.grade,dense_rank()over(partition by c.c_id order by sc.grade desc) sRank 
  from Student s join Score sc on s.s_id=sc.s_id join Course c on sc.c_id=c.c_id
) t where sRank between 2 and 3;

-- 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 课程编号,c.c_name 课程名称,
concat(sum(case when sc.grade>=85 then 1 else 0 end),'人,占',round(sum(case when sc.grade>=85 then 1 else 0 end)/count(1)*100,1),'%')`100-85`,
concat(sum(case when sc.grade>=70 and sc.grade<85 then 1 else 0 end),'人,占',round(sum(case when sc.grade>=70 and sc.grade<85 then 1 else 0 end)/count(1)*100,1),'%')`85-70`,
concat(sum(case when sc.grade>=60 and sc.grade<70 then 1 else 0 end),'人,占',round(sum(case when sc.grade>=60 and sc.grade<70 then 1 else 0 end)/count(1)*100,1),'%')`70-60`,
concat(sum(case when sc.grade<70 then 1 else 0 end),'人,占',round(sum(case when sc.grade<70 then 1 else 0 end)/count(1)*100,1),'%')`0-60`
from Score sc join Course c on sc.c_id=c.c_id
group by sc.c_id;

-- 24、查询学生平均成绩及其名次 
select *,rank()over(order by 平均分 desc) 名次 
from (select s.s_name 姓名,round(avg(ifnull(sc.grade,0)),1) 平均分 
      from Student s left join Score sc on s.s_id=sc.s_id 
      group by s.s_id)t;

-- 25、查询各科成绩前三名的记录
select * from (select sc.s_id,c.c_name,grade,rank()over(partition by sc.c_id order by grade desc) sRank 
               from Score sc join Course c on sc.c_id=c.c_id) t 
where sRank<=3

-- 26、查询每门课程被选修的学生数 
select c.c_id,c.c_name 课程,count(1) 学生数 from Course c 
left join Score sc on sc.c_id=c.c_id
group by c.c_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 学号,st.s_name 姓名 from Student st 
join Score sc on sc.s_id=st.s_id
group by st.s_id having count(1)=2

-- 28、查询男生、女生人数
select s_sex 性别,count(1) 人数 from Student group by s_sex

-- 29、查询名字中含有"风"字的学生信息
select * from Student where s_name like "%风%";

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

-- 31、查询1990年出生的学生名单
select * from Student where 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 编号,c.c_name 课程,avg(sc.grade) 平均分 from Course c
join Score sc on sc.c_id=c.c_id  
group by c.c_id order by avg(sc.grade) 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 学号,st.s_name 姓名,avg(sc.grade) 平均分 from Student st
join Score sc on sc.s_id=st.s_id
group by st.s_id having avg(sc.grade)>=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_name 姓名,sc.grade 分数 from Student st
inner join Score sc on sc.s_id=st.s_id and sc.grade<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.grade 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 st.s_id,st.s_name,c.c_name,sc.grade from Student st
join Score sc on sc.s_id=st.s_id
join Course c on c.c_id=sc.c_id 
where sc.grade>=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.grade from Student st
join Score sc on sc.s_id=st.s_id
join Course c on c.c_id=sc.c_id 
where sc.grade<60

-- 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.grade from Student st
join Score sc on sc.s_id=st.s_id and sc.c_id='01' and sc.grade>=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.grade,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.grade desc limit 1

-- 41、查询各课成绩相同的学生的学生编号、课程编号、学生成绩 
select distinct s.s_id,s.s_name,sc.grade 
from Student s
join Score sc on s.s_id=sc.s_id
join Course c on sc.c_id=c.c_id
where (select count(1) from Score where s_id=s.s_id and grade=sc.grade)=(select count(1) from Course)

-- 42、查询每门课程成绩最好的前两名学生/课程/分数
select s.s_name,c.c_name,sc.grade 
from (select * from (select s_id,c_id,grade,rank()over(partition by c_id order by grade desc) tRank from Score)t where tRank<=2) sc 
join Student s on s.s_id=sc.s_id 
join Course c on c.c_id=sc.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 课程号,count(1) 人数 from Score sc
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 
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
join Score sc on sc.s_id=st.s_id,(select @count:=count(1) from Course)t
group by st.s_id having count(1)=@count

-- 46、查询各学生的年龄
select st.*,timestampdiff(year,st.s_birth,now()) 年龄 from Student st

-- 47、查询本周过生日的学生
-- 方法1
select * from Student where week(concat(year(now()),date_format(s_birth,'-%m-%d')))=week(now());
-- 方法2
select * from Student, (select @monday:=date_add(now(),interval -weekday(now()) day),@sunday:=date_add(now(),interval 6-weekday(now()) day))t
where date_format(s_birth,'%m%d')>=date_format(@sunday,'%m%d') and date_format(s_birth,'%m%d')<=date_format(@monday,'%m%d')

-- 48、查询下周过生日的学生
select * from Student, (select @monday:=date_add(now(),interval 7-weekday(now()) day),@sunday:=date_add(now(),interval 13-weekday(now()) day))t
where date_format(s_birth,'%m%d')>=date_format(@sunday,'%m%d') and date_format(s_birth,'%m%d')<=date_format(@monday,'%m%d')

-- 49、查询本月过生日的学生
select * from Student where month(now())=month(s_birth)

-- 50、查询下月过生日的学生
select * from Student where month(s_birth)=date_add(now(),interval 1 month)