MySQL练习50题

这是网上的练习，花了点时间用MySQL做了一下。

初始化数据库：

create database db50issues;

use db50issues;

create table Student(sid 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');

select * from Student;

create table Course(Cid varchar(10),Cname nvarchar(10),Rteacher 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');

select * from Course;

create table Teacher(Tid varchar(10),Tname nvarchar(10));
insert into Teacher values('01' , N'刘备');
insert into Teacher values('02' , N'孙权');
insert into Teacher values('03' , N'曹操');

select * from Teacher;

create table Score(Sid varchar(10),Cid varchar(10),score decimal(18,1));
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);

select * from Score;

 

 

题目与解答：

select * from Student;
select * from Course;
select * from Teacher;
select * from Score;
#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 A.Cid as Aid,A.score as Ascore,B.Cid as Bid,B.score as Bscore,D.* from
(select * from Score where Cid = '01') A
left join
(select * from Score where Cid = '02') B
on A.Sid= B.Sid
left join 
Student D
on D.sid = A.Sid 
where A.score > B.score;

#1.1 查询同时存在" 01 "课程和" 02 "课程的情况
select * from
(select * from Score where Cid = '01') A
,
(select * from Score where Cid = '02') B
where A.Sid= B.Sid;

#1.2 查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为null)  
select * from
(select * from Score where Cid = '01') A
left join
(select * from Score where Cid = '02') B
on A.Sid= B.Sid;

#1.3 查询不存在" 01 "课程但存在" 02 "课程的情况
select * from
(select * from Score where Cid = '01') A
right join
(select * from Score where Cid = '02') B
on A.Sid= B.Sid;

#2. 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 B.Sname , C.* from
(select A.sid ,avg(A.score) savg from score A group by A.sid ) C
left join 
student B
on B.sid = C.sid    
where savg >= 60;


#3. 查询在 score 表存在成绩的学生信息
select * from student A
where A.sid in (select sid from score);

#4. 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(没成绩的显示为 null )
select * from
student B
left join
(select A.sid, count(*),sum(score) from 
score A group by A.sid) C
on B.sid = C.sid;

#4.1 查有成绩的学生信息
select * from student where sid in ( select sid from score);

#5. 查询「曹」姓老师的数量 
select count(*) as num from teacher where tname like '曹%';

#6. 查询学过「张三」老师授课的同学的信息 
select * from student C where C.sid in
(select sid from score where cid in 
(select B.cid from course B where B.Rteacher in 
(select A.tid from Teacher A where A.tname = '曹操')));

#7. 查询没有学全所有课程的同学的信息 
select sid,count(*) cc from score
group by sid 
having cc !=(select count(*) from course);

#8. 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 * from student where sid in 
(select distinct sid from score where cid in 
(select cid from score where sid ='01'));

#9. 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 * from student where sid not in 
(select distinct sid from score where cid in 
(select cid from score where sid ='01'));


#10. 查询没学过"张三"老师讲授的任一门课程的学生姓名 
select sname from student where sid not in 
(select sid from score where cid in
(select cid from course where Rteacher in 
(select tid from teacher where tname = '孙权')));

#11. 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 B.sid,B.sname, avg(A.score) AVGScore from score A left join student B on A.sid = B.sid
where A.score < 60 
group by A.sid having count(*) > 1;

#12. 检索" 01 "课程分数小于 60，按分数降序排列的学生信息
select * from score A left join student B on A.Sid = B.sid
where A.cid = '01' and A.score < 60
order by A.score desc;

#13.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 
#(从列信息变成行信息)
select B.sid,B.sname ,
max(case when A.cid = '01' then A.score else 0 end) as '01',
max(case when A.cid = '02' then A.score else 0 end) as '02',
max(case when A.cid = '02' then A.score else 0 end) as '03',
avg(A.score)
from score A right join student B on A.sid = B.sid
group by B.sid 
order by avg(A.score) desc;

#14. 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
#   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


#15. 按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺
select * , @curRank := @curRank + 1 rank
from score a ,(select @curRank := 0 ) b
order by a.score;

#15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次
select a.* ,
CASE 
WHEN @prevRank = a.score THEN @curRank 
WHEN @prevRank := a.score THEN @curRank := @curRank + 1
END AS rank
from score a ,(select @curRank := 0 , @prevRank :=null ) b
order by a.score desc;

#16.  查询学生的总成绩，并进行排名，总分重复时保留名次空缺
select c.*,@curRank := @curRank + 1 as rank from 
(select a.sid,a.sname,sum(score) as scores
from (student a  right join score b on a.sid = b.sid) 
group by a.sid ) c , (select @curRank := 0) d 
order by scores desc;

#16.1 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺
select c.*,
CASE 
WHEN @prevRank = c.scores THEN @curRank 
WHEN @prevRank := c.scores THEN @curRank := @curRank + 1
END AS rank
from 
(select a.sid,a.sname,sum(score) as scores
from (student a  right join score b on a.sid = b.sid) 
group by a.sid ) c , (select @curRank := 0 , @prevRank :=null ) d 
order by scores desc;

#17. 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]，[60-0] 及所占百分比  
select A.cid , B.cname
        , sum(case when score >=85 and score <=100 then 1 else 0 end ) '[100-85]'
        ,sum(case when score >=85 and score <=100 then 1 else 0 end )*1.00/count(*) as '[100-85]percent'
        , sum(case when score < 85 and score >= 70 then 1 else 0 end ) '(85-70]'
        ,sum(case when score < 85 and score >= 70 then 1 else 0 end )*1.00/count(*) as '(85-70]percent'
        , sum(case when score < 70 and score >= 60 then 1 else 0 end ) '(70-60]'
        ,sum(case when score < 70 and score >= 60 then 1 else 0 end )*1.00/count(*) as '(85-70]percent'
        , sum(case when score < 60 and score >= 0 then 1 else 0 end ) '(60-0]'
        ,sum(case when score < 60 and score >= 0 then 1 else 0 end )*1.00/count(*) as '(85-70]percent'
        ,count(*) as counts
from score A left join course B on A.cid = B.cid
group by cid;

#18. 查询各科成绩前三名的记录
select * from score a where (select COUNT(*)from score where cid=a.cid and score>a.score)<3  
    order by a.cid, a.score desc;

select a.sid, a.cid,a.score from score a 
left join score b on a.cid = b.cid and a.score < b.score
group by a.sid , a.cid having count(b.sid) < 3
order by a.cid ,a.score desc;

#19. 查询每门课程被选修的学生数
select   a.cid , b.cname ,count(*) as num  from score a left join course b on a.cid = b.cid
group by a.cid;

#20. 查询出只选修两门课程的学生学号和姓名  
select a.sid,b.sname from score a left join student b on a.sid = b.sid 
group by a.sid having count(*) = 2;

#21. 查询男生、女生人数 
select s.ssex, count(*) from student s 
group by s.ssex;

#22. 查询名字中含有「风」字的学生信息 
select * from student s 
where s.sname like '%风%';

#23. 查询同名同性学生名单，并统计同名人数 
select a.sname,a.ssex , count(*) num 
from student a 
group by a.sname,a.ssex having num > 1;

#24.查询 1990 年出生的学生名单 
select * from student s 
where year(s.sage) = 1990;

#25. 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 s.cid, avg(s.score) as scoreAVG  from score s 
group by s.cid
order by scoreAVG desc , s.cid;

#26. 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.sid,a.sname, avg(b.score) as scoreAVG from student a left join score b on a.sid = b.sid
group by a.sid having scoreAVG >= 85;

#27. 查询课程名称为「数学」，且分数低于 60 的学生姓名和分数
select a.sname , b.score from student a left join score b on a.Sid = b.sid
where b.cid = (select cid from course where Cname = '数学' ) and b.score < 60;

#28. 查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）
select * from 
student a left join score b on a.sid = b.sid 
left join course c on c.cid = b.cid;

#29. 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 b.sname,c.Cname,a.score from score a left join student b on a.sid = b.sid
left join course c on a.cid = c.cid
where a.score >70;

#30. 查询不及格的课程
select * from score where score < 60;

#31. 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 a.sid,b.sname,a.score from score a left join student b on a.sid = b.sid 
left join score c on a.cid = c.cid 
where a.score > 80 and a.cid = '01';

#32. 求每门课程的学生人数  
select cid,count(*) as num from score 
group by cid ;

#33. 成绩不重复，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 a.*, max(b.score) from student a left join score b on a.sid = b.sid 
left join course c on b.cid = c.Cid
left join teacher d on c.Rteacher = d.Tid 
where d.Tname = '刘备';

select a.*,b.score from student a left join score b on a.sid=b.sid
where cid = (select Cid from course where Rteacher = ( select Tid from teacher where Tname = '刘备'))
order by b.score desc limit 1;

#34. 成绩有重复的情况下，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 * from
(select dd.*,
CASE 
WHEN @prevRank = dd.score THEN @curRank 
WHEN @prevRank := dd.score THEN @curRank := @curRank + 1
END AS rank
 from (select a.*,b.score from
student a 
left join score b on a.sid = b.sid 
left join course c on b.cid = c.Cid
left join teacher d on c.Rteacher = d.Tid where d.Tname = '刘备' ) dd,(select @curRank := 0 , @prevRank :=null ) ff 
order by score desc) as dddddddd
where rank = 1;

#35. 查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩
select distinct a.sid, a.cid, a.score from score a join score b 
where a.cid != b.cid and a.score = b.score and a.sid != b.sid
order by a.sid, a.cid, a.score;


#36. 查询每门功成绩最好的前两名
select * from score a
where (select count(*) from score b where a.cid = b.cid and a.score < b.score ) < 2
order by a.cid , a.score desc;

#37.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 a.Cid, count(*) as num from 
course a left join score b on a.Cid = b.cid
group by a.Cid having num > 5
order by num,a.Cid;

#38. 检索至少选修两门课程的学生学号   
select distinct sid from score
group by sid having count(*) > 1;

#39. 查询选修了全部课程的学生信息   
select * from (
select sid,count(*) as num from score
group by sid ) b
where num = (select count(*) from course) ;
      
#40. 查询各学生的年龄，只按年份来算  
select *, year(now()) - year(sage) as yy from student ;

#41. 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一  


#42.查询本周过生日的学生 
select * from
(select * , week(sage), month(sage),day(sage),
week(str_to_date(concat_ws(',',year(now()),month(sage),day(sage)),'%Y,%m,%d')) as w  from student) A
where w = week(now());

#43. 查询下周过生日的学生 
select * from
(select * , week(sage), month(sage),day(sage),week(now()),
week(str_to_date(concat_ws(',',year(now()),month(sage),day(sage)),'%Y,%m,%d')) as w  from student) A
where w + 2 = week(now());

#44. 查询本月过生日的学生
select * , month(sage),month(now()) from student
where month(sage) = month(now());

#45. 查询下月过生日的学生
select * , month(sage),month(now()) from student
where month(sage) = month(now()) + 2;