/*--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--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create table Student(        S varchar(10),        Sname nvarchar(10),        Sage datetime,        Ssex nvarchar(10)        );insert into Student values(‘01‘ , ‘‘ , ‘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‘);Select * from Student;--2.课程表 --Course(C,Cname,T) --C --课程编号,Cname 课程名称,T 教师编号create table Course(        C varchar(10),        Cname nvarchar(10),        T varchar(10)        )insert into Course values(‘01‘ , ‘语文‘ , ‘02‘);insert into Course values(‘02‘ , ‘数学‘ , ‘01‘);insert into Course values(‘03‘ , ‘英语‘ , ‘03‘);--3.教师表 --Teacher(T,Tname) --T 教师编号,Tname 教师姓名create table Teacher(T varchar(10),Tname nvarchar(10));insert into Teacher values(‘01‘ , ‘张三‘);insert into Teacher values(‘02‘ , ‘李四‘);insert into Teacher values(‘03‘ , ‘王五‘);--4.成绩表 --SC(S,C,score) --S 学生编号,C 课程编号,score 分数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--没有考试的情况下算零分吗？--select a.* , b.score as ‘课程01的分数‘,c.score as ‘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 > c.score) or (isnull(c.score) and not isnull(b.score)) ;select a.* ,b.score as ‘01score‘,c.score as ‘02score‘ 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 > c.score;--1.1、查询同时存在"01"课程和"02"课程的情况select a.* ,b.score as ‘课程01的分数‘,c.score as ‘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 not isnull(b.score) and not isnull(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 as ‘课程01的分数‘,c.score as ‘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)--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 a.* , b.score as‘课程01的分数‘,c.score as ‘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 as‘课程01的分数‘,c.score as ‘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) and not isnull(c.score)) or b.score < 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 , avg(b.score) as ‘avg‘ from Student a,SC b where a.s = b.sgroup by a.s,a.Sname having   avg(b.score) > 60 order by a.s--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select a.s,a.Sname , avg(b.score) as ‘avg‘ from Student a,SC b where a.s = b.sgroup by a.s,a.Sname having   avg(b.score) < 60 order by a.s;-- 不能够确认是否只有两门课select a.s,a.Sname ,sum(b.score) as ‘sum‘ from student a,sc b where a.s = b.s group by a.s ,a.sname having sum(b.score) < 60* count(b.score);--- 每一个同学选择课程的数目select a.s,a.sname, count(b.score) as ‘选课的门数‘ from student a,sc b where a.s = b.sgroup by a.s,a.sname--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。---有一门的成绩就算是有成绩select a.S , a.Sname from Student a left join sc b on a.S = b.S where isnull(b.score)--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 a.S as ‘学生编号‘, a.Sname as ‘学生姓名‘, count(b.C) as ‘选课总数‘, sum(score) as ‘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 as ‘学生编号‘, a.Sname as ‘学生姓名‘, count(b.C) as ‘选课总数‘, sum(score) as ‘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1select * from Teacher ;select count(Tname) as ‘"李"姓老师的数量‘ from Teacher where Tname like ‘李%‘--方法2select count(Tname) as ‘"李"姓老师的数量‘ from Teacher where left(Tname,1) = ‘李‘--7、查询学过"张三"老师授课的同学的信息  select distinct Student.* ,SC.C,Teacher.Tname from Student , SC , Course , Teacher where Student.S = SC.S and SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = ‘张三‘order by Student.S;select * from Course;select * from Teacher;--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 = ‘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1select 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2select Student.* from Student , SC where Student.S = SC.S and SC.C = ‘02‘ and exists (        Select SC.s from SC SC_2 where SC_2.S = SC.S and SC_2.C = ‘01‘        ) order by Student.S;--方法3 不是很明白 not in/in / exists 判断的依据是什么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1select a.* from Student a ,SC b where a.s = b.s and b.c=‘01‘ and not exists (        Select 1 from SC SC_2 where SC_2.S = b.S and SC_2.C = ‘02‘)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2select 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.* ,count(C),(select count(C) from Course) as‘总数‘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) --11.2select Student.*  ,count(C),(select count(C) from Course) as‘总数‘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-- 首先是选的课全部在01同学的选的课的范围内-- 选的课的门数是相同的 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 = ‘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.c when ‘01‘ then b.score else null end) as ‘语文‘,       max(case c.c when ‘02‘ then b.score else null end) as ‘数学‘,       max(case c.c when ‘03‘ then b.score else null end) as ‘英语‘,       cast(avg(b.score) as decimal(18,2)) 平均分from Student a left join SC b on a.S = b.Sleft join Course c on b.C = c.Cgroup by a.S , a.Snameorder by 平均分 descselect * from course --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1select 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 nwhere m.C = n.Cgroup by m.C , m.Cnameorder by m.C--方法2select 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.* ,  ((select count(1) from SC where C = t.C and score > t.score) + 1) as pc from sc t order by t.C ,pc--Score重复时合并名次select t.* ,(select count(distinct score) from SC where C = t.C and score >= t.score) as  px  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 as‘学生编号‘ ,        m.Sname as ‘学生姓名‘ ,       sum(score) as ‘总成绩‘from Student m left join SC n on m.S = n.S group by m.S , m.Snameorder by ‘总成绩‘ desc--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_scorefrom Teacher m , Course n , SC owhere m.T = n.T and n.C = o.Cgroup by m.T , m.Tnameorder 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--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.Cnameorder by Course.C--纵向显示1(显示存在的分数段)select m.C as ‘课程编号‘ , m.Cname as ‘课程名称‘ ,(  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) as  分数段   ,   count(1) 数量 from Course m , sc nwhere 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 nwhere 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 nwhere 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 nwhere 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.* , (select count(1) as px from --(--  select m.S as ‘学生编号‘ , --         m.Sname as ‘学生姓名‘ ,--         isnull(cast(avg(score) as decimal(18,2))) as ‘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 as‘学生编号‘ , --         m.Sname as ‘学生姓名‘ ,--         isnull(cast(avg(score) as decimal(18,2))) as ‘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 n.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.Snamefrom Student , SC where Student.S = SC.S group by Student.S , Student.Snamehaving count(SC.C) = 2order by Student.S --28、查询男生、女生人数 select count(Ssex) as 男生人数 from Student where Ssex = ‘男‘select count(Ssex) as 女生人数 from Student where Ssex = ‘女‘select sum(case when Ssex = ‘男‘ then 1 else 0 end) as ‘男生人数‘,sum(case when Ssex = ‘女‘ then 1 else 0 end)as ‘女生人数‘ from student--29、查询名字中含有"风"字的学生信息select * from student where sname like  ‘%风%‘--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 --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_scorefrom 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_scorefrom Student a , sc bwhere a.S = b.Sgroup by a.S , a.Snamehaving 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 , scorefrom Student , SC , Course where SC.S = Student.S and SC.C = Course.C and Course.Cname = ‘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.Cgroup by  Course.C , Course.Cnameorder 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--40.2 当最高分出现多个时select Student.* , Course.Cname , SC.C , SC.score  from Student, SC , Course , Teacherwhere Student.S = SC.S and SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N‘张三‘ andSC.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1select 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2select 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.Cgroup by  Course.C , Course.Cnamehaving count(*) >= 5order 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) >= 2order 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(now(),sage) as ‘存在的天数‘ 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drop table  Student,Course,Teacher,SC