MySQL50道典型案例

MySQL经典题50道

建表前准备工作 解决this is incompatible with sql_mode=only_full_group_by问题
找到MySQL配置文件 将下列代码加入其中 保存后重启MySQL服务 即可解决
代码 	sql_mode=STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

学生表建表

create table Student(
SId varchar(10),
Sname varchar(10),
Sage datetime,
Ssex varchar(10)
);

课程表建表

create table Course(
CId varchar(10),
Cname nvarchar(10),
TId varchar(10)
);

教师表建表

create table Teacher(
TId varchar(10),
Tname varchar(10)
);

成绩表建表

create table SC(
SId varchar(10),
CId varchar(10),
score decimal(18,1)
);

四表添加数据

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' , '1990-12-20' , '男');
insert into Student values('04' , '李云' , '1990-12-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-01-01' , '女');
insert into Student values('07' , '郑竹' , '1989-01-01' , '女');
insert into Student values('09' , '张三' , '2017-12-20' , '女');
insert into Student values('10' , '李四' , '2017-12-25' , '女');
insert into Student values('11' , '李四' , '2012-06-06' , '女');
insert into Student values('12' , '赵六' , '2013-06-13' , '女');
insert into Student values('13' , '孙七' , '2014-06-01' , '女');

insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');

insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

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);
	

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 * from Student RIGHT JOIN (
	select t1.SId, cl1, cl2 from
		(select SId, score as cl1 from sc where sc.CId = '01')as t1, 
		(select SId, score as cl2 from sc where sc.CId = '02')as t2
where t1.SId = t2.SId AND t1.cl1 > t2.cl2
)c on Student.SId = c.SId;

1.1查询同时存在" 01 “课程和” 02 "课程的情况

select * from 
(select * from sc where sc.CId = '01') as t1, 
(select * from sc where sc.CId = '02') as t2
where t1.SId = t2.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 sc where sc.CId = '02') as t2
right join 
	(select * from sc where sc.CId = '01') as t1
on t1.SId = t2.SId;

1.3查询不存在" 01 “课程但存在” 02 "课程的情况

select * from sc
where sc.SId not in 
	(select SId from sc where sc.CId = '01') 
AND sc.CId= '02';

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 s.sid,s.sname,p.avg from 
Student s,(select sid,avg(score) avg from SC GROUP BY sid) p
where s.sid=p.sid and p.avg>=60;

3. 查询在 SC 表存在成绩的学生信息

SELECT DISTINCT student.*
	FROM student,sc WHERE student.SID = sc.SID;

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 student.sid, student.sname,c.coursenumber,c.scoresum
from student,
(select sc.sid, sum(sc.score) as scoresum, count(sc.cid) as coursenumber from sc 
group by sc.sid)c
where student.sid = c.sid;

4.1查有成绩的学生信息

select * from student 
where exists (select sc.sid from sc where student.sid = sc.sid);

5. 查询「李」姓老师的数量

select count(*) from teacher where tname like '李%';

6. 查询学过「张三」老师授课的同学的信息

select student.* from student,teacher,course,sc
where student.sid = sc.sid and course.cid=sc.cid and course.tid = teacher.tid and tname = '张三';

7. 查询没有学全所有课程的同学的信息

select * from student
where student.sid not in (
select sc.sid from sc
group by sc.sid 
having count(sc.cid)= (select count(cid) 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 student.sid in (
			select sc.sid from sc 
				where sc.cid in(
					select sc.cid from sc 
						where sc.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

	group_concat() 函数作用：将组中的字符串连接成为具有各种选项的单个字符串。

select * from student
where sid in (
    select sid from sc
			group by sid
				having group_concat(cid ORDER BY cid) = (
					select group_concat(cid ORDER BY cid)
						from sc where sid = '01') and 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 * from student
where student.sid not in(
    select sc.sid from sc,course,teacher 
    where sc.cid = course.cid
        and course.tid = teacher.tid
        and teacher.tname= "张三"
);

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 student.sid, student.sname, AVG(sc.score) from student,sc
where student.sid = sc.sid and sc.score<60
group by sc.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 student.*, sc.score from student, sc
where student.sid = sc.sid and sc.score < 60 and cid = "01"
ORDER BY sc.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

select *  from sc 
left join (
    select sid,avg(score) as avscore from sc 
    group by sid
    )c 
on sc.sid = c.sid
order by avscore 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

select sc.CId ,max(sc.score)as 最高分,min(sc.score)as 最低分,AVG(sc.score)as 平均分,count(*)as 选修人数,
sum(case when sc.score>=60 then 1 else 0 end )/count(*)as 及格率,
sum(case when sc.score>=70 and sc.score<80 then 1 else 0 end )/count(*)as 中等率,
sum(case when sc.score>=80 and sc.score<90 then 1 else 0 end )/count(*)as 优良率,
sum(case when sc.score>=90 then 1 else 0 end )/count(*)as 优秀率 
from sc
GROUP BY sc.CId
ORDER BY count(*)DESC, sc.CId ASC;

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 a.cid, a.sid, a.score, count(b.score)+1 as rank1
from sc as a 
left join sc as b 
on a.score<b.score and a.cid = b.cid
group by a.cid, a.sid,a.score
order by a.cid, rank1 ASC;

#自定义变量： 申明变量：SET @crank =0;  对变量进行赋值：@crank := @crank +1，赋值操作符   =或:=  使用：查找，比较  运算等 

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.* ,count(b.score)+1 rank1 from sc a left join sc b
on a.cid = b.cid and (a.score < b.score or (a.score = b.score and a.sid > b.sid))
group by a.cid,a.sid
order by a.cid,count(b.score)

16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

SET @crank =0;
SELECT b.studentid, b.a, @crank := @crank +1 AS rank FROM
 (SELECT studentid,SUM(score) AS a FROM student_score GROUP BY studentid ORDER BY a DESC)b ;

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

分数段所占百分比=分数段人数/总人数

select course.cname, course.cid,
sum(case when sc.score<=100 and sc.score>85 then 1 else 0 end) as "[100-85]",
sum(case when sc.score<=85 and sc.score>70 then 1 else 0 end) as "[85-70]",
sum(case when sc.score<=70 and sc.score>60 then 1 else 0 end) as "[70-60]",
sum(case when sc.score<=60 and sc.score>0 then 1 else 0 end) as "[60-0]"
from sc left join course
on sc.cid = course.cid
group by sc.cid;

18.查询各科成绩前三名的记录

统计比自身小的行数有多少行
< 3 也就是取前三

select * from sc where (
select count(*) from sc as a 
where sc.cid = a.cid and sc.score<a.score 
)< 3
order by cid asc, sc.score desc

19.查询每门课程被选修的学生数

select cid, count(sid) from sc group by cid;

20.查询出只选修两门课程的学生学号和姓名

通过sid锁定学生信息
通过sc表进行sid分组查询限制选课科数位2

select student.sid, student.sname from student
where student.sid in
(select sc.sid from sc
group by sc.sid having count(sc.cid)=2
);

21.查询男生、女生人数

select ssex, count(*) from student group by ssex;

22.查询名字中含有「风」字的学生信息

select * from student where student.Sname like '%风%';

23.查询同名同性学生名单，并统计同名人数

查找相同姓名，相同性别的学生，只需要按照姓名，性别进行分组，把相同的人数筛选统计出来

select sname, count(*) from student
group by sname having count(*)>1;

24.查询 1990 年出生的学生名单

select * from student where YEAR(student.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 sc.cid, course.cname, AVG(SC.SCORE) as average from sc, course
where sc.cid = course.cid group by sc.cid 
order by average desc,cid asc;

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 student.sid, student.sname, AVG(sc.score) as aver from student, sc
where student.sid = sc.sid
group by sc.sid
having aver > 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 student.sname, sc.score from student, sc, course
where student.sid = sc.sid and course.cid = sc.cid and course.cname = "数学" and sc.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 student.sname, cid, score from student
left join sc on student.sid = sc.sid;

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 student.sname, course.cname,sc.score from student,course,sc
where sc.score>70 and student.sid = sc.sid and sc.cid = course.cid;

30.查询不及格的课程

select cid from sc where score< 60
group by cid;
select DISTINCT sc.CId from sc where sc.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 student.sid,student.sname from student,sc
where cid="01" and score>=80 and student.sid = sc.sid;

32.求每门课程的学生人数

select sc.CId,count(*) as 学生人数
from sc GROUP BY sc.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

得先知道张三教的课程cid，要获取cid则需要通过name进行判断
接下来限制条件便是cid in 张三老师的cid就可以了

select student.*, sc.score, sc.cid from student, teacher, course,sc 
where teacher.tid = course.tid and sc.sid = student.sid and sc.cid = course.cid
	and teacher.tname = "张三" and sc.score = (
    select Max(sc.score)  from sc,student, teacher, course
    where teacher.tid = course.tid and sc.sid = student.sid and sc.cid = course.cid
    and teacher.tname = "张三"
);

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

需要改题

UPDATE sc SET score=90
where sid = "05"
and cid ="02";

代码同33题

36.查询每门功成绩最好的前两名

select a.sid,a.cid,a.score from sc as a 
left join sc as b 
on a.cid = b.cid and a.score<b.score
group by a.cid, a.sid
having count(b.cid)<2
order by a.cid;

37.统计每门课程的学生选修人数（超过 5 人的课程才统计）

select sc.cid, count(sid) as sl from sc
group by cid having sl >5;

38.检索至少选修两门课程的学生学号

select sid, count(cid) as sl from sc
group by sid having sl>=2;

39.查询选修了全部课程的学生信息

select * from student
where sid in (
    select sid from sc
			group by sid
				having group_concat(cid ORDER BY cid) = (
					select group_concat(cid ORDER BY cid)
						from sc where sid = '01') and sid != '01');

40.查询各学生的年龄，只按年份来算

select student.* from sc ,student 
where sc.SId=student.SId
GROUP BY sc.SId HAVING count(*) = (select DISTINCT count(*) from course );

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

select student.SId as 学生编号,student.Sname  as  学生姓名,
TIMESTAMPDIFF(YEAR,student.Sage,NOW()) as 学生年龄 from student;

42.查询本周过生日的学生

select * from student 
where WEEKOFYEAR(student.Sage)=WEEKOFYEAR(NOW());

43.查询下周过生日的学生

select * from student 
where WEEKOFYEAR(student.Sage)=WEEKOFYEAR(NOW())+1;

44.查询本月过生日的学生 无4月

select * from student 
where MONTH(student.Sage)=MONTH(NOW());

45.查询下月过生日的学生 改题 下个月

select * from student 
where MONTH(student.Sage)=MONTH(NOW())+1;