题记：一直在写各种sql查询语句，最长的有一百多行，自信什么需求都可以接，可。。。。。。，想了想，可能一直在固定的场景下写，平时也是以满足实际需求为目的，竟不知道应试的题都是怎么出的，又应该怎么做。遂找来一些笔试题来练习。
有四张表如下格式存储：
--1、查询“001”课程比“002”课程成绩高的所有学生的学号；
select t1.s# from
(select s#,c#,score from sc where c# = 001) t1 inner join (select s#,c#,score from sc where c# = 002) t2
on t1.s#=t2.s#
where t1.score > t2.score
--2、查询平均成绩大于60分的同学的学号和平均成绩；
select s#,avg(score)
from sc
group by s# having avg(score)>60
--3、查询所有同学的学号、姓名、选课数、总成绩；
select student.s#,student.sname,count(sc.c#),sum(sc.score)
from student left join sc on student.s#=sc.s#
group by student.s#,student.sname
--4、查询姓“李”的老师的个数；
select count(t#)
from teacher
where tname like '李%'
--5、查询没学过“叶平”老师课的同学的学号、姓名；
select t1.s#,t1.sname
from student t1
left join sc t2 on t1.s#=t2.s#
left join course t3 on t2.c#=t3.c#
left join teacher t4 on t3.t#=t4.t#
where t4.tname != '叶平'
--6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
select t0.s#,t0.sname
from student t0
inner join (select s#,c#,score from sc where c# = 001) t1
on t0.s#=t1.s#
inner join (select s#,c#,score from sc where c# = 002) t2
on t0.s#=t2.s#
--7、查询学过“叶平”老师所教的所有课的同学的学号、姓名；
select t1.s#,t1.sname
from student t1
left join sc t2 on t1.s#=t2.s#
left join course t3 on t2.c#=t3.c#
left join teacher t4 on t3.t#=t4.t#
where t4.tname = '叶平'
--8、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名；
select t0.s#,t0.sname
from student t0
inner join (select s#,c#,score from sc where c# = 001) t1
on t0.s#=t1.s#
inner join (select s#,c#,score from sc where c# = 002) t2
on t0.s#=t2.s#
where t2.score<t1.score
--9、查询所有课程成绩小于60分的同学的学号、姓名；
select t1.s#,t1.sname
from student t1
inner join (select s#,count(c#),count(if(score<60,c#,null)) from sc group by s# having count(c#) = count(if(score<60,c#,null))) t2
on t1.s#=t2.s#
--10、查询没有学全所有课的同学的学号、姓名；
select t1.s#,t1.sname
from student t1 inner join sc t2 on t1.s#=t2.s#
group by t1.s#,t1.sname
having count(c#) < (select count(c#) from course)
--11、查询至少有一门课与学号为“1001”的同学所学相同的同学的学号和姓名；
select distinct t1.s#,t1.sname
from student t1 inner join sc t2 on t1.s#=t2.s#
left semi join (select c# from sc where s#=1001) t3 on t2.c#=t3.c#
--12、查询至少学过学号为“001”同学所有一门课的其他同学学号和姓名；
--13、查询和“1002”号的同学学习的课程完全相同的其他同学学号和姓名；
select t1.s#,t3.sname
from sc t1
inner join sc t2
on t1.c#=t2.c#
left join student t3
on t1.s#=t3.s#
where t2.s#=1002
group by t1.s#
having count(distinct t1.c#) = count(distinct t2.c#)
--14、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分
select c#,max(score),min(score)
from sc
group by c#
--15、按各科平均成绩从低到高和及格率的百分数从高到低顺序
select c#,ave,count_g/count_all
from (select c#,
average(score) ave,
count(if(score>=60,s#,null)) count_g,
count(s#) count_all
from sc
group by c#) t1
order by ave,count_g/count_all desc
--16、查询如下课程平均成绩和及格率的百分数(用"1行"显示): 企业管理（001），马克思（002），OO&UML （003），数据库（004）
select c#,ave,count_g/count_all
from
(select c#,
average(score) ave,
count(if(score>=60,s#,null)) count_g,
count(s#) count_all
from sc
where c# in (001,002,003,004)
group by c#) t1
--17、查询不同老师所教不同课程平均分从高到低显示
select t2.cname,t3.tname,avg(t1.score)
from sc t1
inner join course t2 on t1.c#=t2.c#
inner join teacher t3 on t2.t#=t3.t#
group by t2.cname,t3.tname
order by avg(t1.score) desc
--18、查询如下课程成绩第 3 名到第 6 名的学生成绩单：企业管理（001），马克思（002），UML （003），数据库（004）
select * from
(select t1.s#,t1.sname,t2.c#,t2.score,row_number() over(partition by t2.c# order by t2.score desc) num
from student t1
inner join sc t2 on t1.s#=t2.s#
where c# in (001,002,003,004)) t
where t.num >=3 and t.num<=6
--19、统计列印各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]
select t1.c#,t2.cname,case when t1.score >=85 then [100-85] when (t1.score <85 and t1.score >=70) then [85-70] when (t1.score <70 and t1.score >=60) then [70-60] when t1.score <60 then [ <60] end as score, count(t1.s#)
from sc t1
inner join course t2 on t1.c#=t2.c#
group by t1.c#,t2.cname
--20、查询学生平均成绩及其名次
select t1.s#,t1.sname,avg(t2.score),row_number() over(order by avg(t2.score)) as ranking
from student t1
inner join sc t2 on t1.s#=t2.s#
--21、查询各科成绩前三名的记录:(不考虑成绩并列情况)
select * from
(select t1.s#,t1.sname,t2.c#,t2.score,row_number() over(partition by t2.c# order by t2.score desc) num
from student t1
inner join sc t2 on t1.s#=t2.s#
) t
where t.num <=3
--22、查询每门课程被选修的学生数
select c#,count(s#)
from sc group by c#
--23、查询出只选修了一门课程的全部学生的学号和姓名
select t1.s#,t2.sname
from sc t1
inner join student t2 on t1.s#=t2.s#
where count(t1.c#)=1
group by t1.s#,t2.sname
--24、查询男生、女生人数
select ssex,count(s#)
from student group by ssex
--25、查询姓“张”的学生名单
select s#,sname
from student
where sname like '张%'
--26、查询同名同性学生名单，并统计同名人数
select sname,count(s#)
from student
where count(s#)>1
group by sname
--27、1981年出生的学生名单(注：Student表中Sage列的类型是datetime)
select s#,sname
from student
where datediff(year,today,sage)=1981
--28、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列
select c#,avg(score) from sc
group by c# order by avg(score),c# desc
--29、查询平均成绩大于85的所有学生的学号、姓名和平均成绩
select t1.s#,t2.sname,avg(t1.score)
from sc t1 inner join student t2 on t1.s#=t2.s#
group by t1.s# having avg(t1.score)>85
--30、查询课程名称为“数据库”，且分数低于60的学生姓名和分数
select t0.sname,t1.score
from student t0
inner join sc t1 on t0.s#=t1.s#
inner join course t2 on t1.c#=t2.c#
where t2.cname = '数据库' and t1.score<60
--31、查询所有学生的选课情况；
select t1.s#,t1.sname,t2.c#,t3.cname
from student t1
left join sc t2 on t1.s#=t2.s#
inner join course t3 on t2.c#=t3.c#
--32、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 t1.sname,t3.cname,t2.score
from student t1
inner join sc t2 on t1.s#=t2.s#
inner join course t3 on t2.c#=t3.c#
where t2.score>70
--33、查询不及格的课程，并按课程号从大到小排列
select c#,avg(score)
from sc
group by c#
order by avg(score) desc
having avg(score)<60
--34、查询课程编号为003且课程成绩在80分以上的学生的学号和姓名；
select t1.s#,t1.sname
from student t1
inner join sc t2 on t1.s#=t2.s#
inner join course t3 on t2.c#=t3.c#
where t3.c#=003 and t2.score>80
--35、求选了课程的学生人数
select count(distinct s#)
from sc
--36、查询选修“叶平”老师所授课程的学生中，成绩最高的学生姓名及其成绩
select t1.sname,max(t2.score)
from student t1 inner join sc t2 on t1.s#=t2.s#
inner join course t3 on t2.c#=t3.c#
inner join teacher t4 on t3.t#=t4.t#
where t4.tname='叶平'
group by t1.sname
--37、查询各个课程及相应选修人数
select c#,count(s#)
from sc
group by c#
--38、查询不同课程成绩相同的学生的学号、课程号、学生成绩
select t1.s#,t1.c#,t2.c#,t1.score
from sc t1
inner join sc t2 on t1.s#=t2.s#
where t1.score=t2.score and t1.c#<>t2.c#
--39、查询每门课程成绩最好的前两名
select c#,s# from
(select c#,s#,score,row_number() over(partition by c# order by score desc) num
from sc) t
where t.num=2
--40、统计每门课程的学生选修人数（超过10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，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 c#,count(s#)
from sc
group by c#
order by count(s#) desc,c#
having count(s#)>10
--41、检索至少选修两门课程的学生学号
select s#
from sc
group by s#
having count(c#)>=2
--42、查询全部学生都选修的课程的课程号和课程名
select t1.c#,t2.cname
from sc t1 inner join course t2 on t1.c#=t2.c#
group by t1.c#,t2.cname
having count(s#)=(select count(s#) from student)
--43、查询没学过“叶平”老师讲授的任一门课程的学生姓名
select
from student s
left join (select t1.sname
from student t1 inner join sc t2 on t1.s#=t2.s#
inner join course t3 on t2.c#=t3.c#
inner join teacher t4 on t3.t#=t4.t#
where t4.tname='叶平') t
on s.sname=t.sname
where t.sname is null
--44、查询两门以上不及格课程的同学的学号及其平均成绩
select s#,avg(score)
from sc
group by s#
having count(if(score<60,c#,null))>2
--45、检索“004”课程分数小于60，按分数降序排列的同学学号
select s#,score
from sc
where c#=004 and score<60
order by score desc
以上，均为自己所写，如有错误，敬请指正