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  • 2021-05-12 23:05:52

    50个经典Sql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)》。



    对我有用[9]丢个板砖[0]引用举报管理TOP 回复次数:1043


    dawugui
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    等 级:
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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
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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

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