练习数据

数据表

–1.学生表 Student(SId,Sname,Sage,Ssex)–SId 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

–2.课程表 Course(CId,Cname,TId) --CId --课程编号,Cname 课程名称,TId 教师编号

–3.教师表 Teacher(TId,Tname) --TId 教师编号,Tname 教师姓名

–4.成绩表 SC(SId,CId,score) --SId 学生编号,CId 课程编号,score 分数

创建测试数据

学生表Student

create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(10));
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' , '1990-05-20' , '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('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' , '2017-12-30' , '女');
insert into Student values('12' , '赵六' , '2017-01-01' , '女');
insert into Student values('13' , '孙七' , '2018-01-01' , '女');

课程表Course

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

教师表 Teacher

create table Teacher(TId varchar(10),Tname varchar(10));
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

成绩表 SC

create table SC(SId varchar(10),CId 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);

练习题目

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

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 )

1.3 查询不存在" 01 “课程但存在” 02 "课程的情况

select a.*,b.cid,b.score
from sc a inner join sc b
where a.sid=b.SId and a.CId='01'and b.CId='02' and a.score>b.score;
#1.1
select a.sid,a.score,b.sid,b.score
from sc a inner join sc b
where a.sid=b.sid and a.CId='01'and b.CId='02'
#1.2
select a.*,b.cid,b.score
from (select * from sc where cid='01' )a left join (select * from sc where cid='02') b
on a.sid=b.sid
#1.3
select *
from sc 
where sc.cid not in (select cid from sc where cid='01')
and sc.cid='02'

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 student.sid,student.sname,a.avg_score
from  student 
inner join(
	select sc.sid,avg(score) avg_score
	from sc
	GROUP BY sc.sid
	HAVING avg(sc.score)>=60)a 
on a.SId=student.sid

查询在 SC 表存在成绩的学生信息
```
select b.*
from
(select sid
from sc 
GROUP BY sid) a
INNER  JOIN student b
on a.sid=b.sid
```
group by 只能查询分组字段，其它字段只能以聚合函数的形式被查询出来
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 )

4.1 查有成绩的学生信息
```
select 
a.sid,
a.sname,
count(b.cid) as counts,
sum(b.score) as sum_score
from 
student a LEFT JOIN sc b
on a.sid=b.sid
GROUP BY a.sid
#4.1
```

查询「李」姓老师的数量

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

查询学过「张三」老师授课的同学的信息

select * from course a inner join teacher b on a.tid=b.tid;

select * from sc a inner join (select a.*,b.tname from course a inner join teacher b on a.tid=b.tid)b on a.cid=b.cid;

select a.*,b.tname from student a inner join (select a.*,b.tname from sc a inner join (select a.*,b.tname from course a inner join teacher b on a.tid=b.tid)b on a.cid=b.cid)b on a.sid=b.sid having b.tname='张三';

查询没有学全所有课程的同学的信息

select b.*
from sc a
inner join student b
on a.sid=b.sid
group by a.sid
having count(1)<(select count(1) from course)

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 a.* from student a right join(
select sid from sc where cid in(select cid
from sc 
where sid='01'))b
on a.sid=b.sid
group by a.sid
having a.sid != '01'

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 b.*
from (select * from sc where sid not in (select sid from sc where cid not in (select cid from sc where sid='01')))a
left join student b
on a.sid=b.sid
group by a.sid
having count(cid)=(select count(1) from sc where sid='01');

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 sid not in
(select c.sid from teacher a right join course b
on a.tid=b.tid
right join sc c
on c.cid= b.cid
where tname='张三')

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 sc.sid, sname ,avg(score) avg_score
from sc left join student 
on sc.sid=student.sid 
where score<60 
group by sid 
having count(1)>1

检索" 01 "课程分数小于 60，按分数降序排列的学生信息

select score,b.* from
sc a left join student b
on a.sid=b.sid where a.cid='01' and score<60 group by a.sid
order by score desc

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 a.* ,avg_score from 
sc a left join (select avg(score) avg_score,sid from sc group by sid )b
on a.sid=b.sid
order by avg_score desc

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

#sum(case when score>=60 then 1 else 0 end)/count(1) as 及格率
#sum(case when score>=70 and score<80 then 1 else 0 end)/count(1) as 中等率
#sum(case when score>=80 and score<90 then 1 else 0 end)/count(1) as 优良率
#sum(case when score>=90  then 1 else 0 end)/count(1) as 优秀率
select sc.cid '课程ID',cname '课程name',max(score) '最高分',min(score) '最低分',avg(score) '平均分',count(1) '选修人数',sum(case when score>=60 then 1 else 0 end)/count(1) '及格率',sum(case when score>=70 and score<80 then 1 else 0 end)/count(1) '中等率',sum(case when score>=80 and score<90 then 1 else 0 end)/count(1) '优良率',sum(case when score>=90  then 1 else 0 end)/count(1) '优秀率'
 from sc left join course
 on sc.cid=course.cid
 group by sc.cid
 order by count(1) desc ,sc.cid asc

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 @rank:= 1;
select @rank;

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 sid,cid,score,
@rank:=@rank+1 as rn
from sc,(select @rank:=0) t
order by score desc
#15.1
select sid,cid,score,
case when @sco=score then @rank
		 when @sco:=score then @rank:=@rank+1 end as rn
from sc,(select @rank:=0,@sco:=null) t
order by score desc

查询学生的总成绩，并进行排名，总分重复时保留名次空缺

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 a.*,
@rank:=@rank+1
from
(select sid,sum(score) scos from sc group by sid order by scos desc)a,(select @rank:=0)b
#16.1
select 
a.sid,
@rank:=if(@sco=scos,'',@rank+1) as rank,
@sco:=scos
from
(select sid,sum(score) scos from sc group by sid order by scos desc) a,
(select @sco:=null,@rank:=0)b

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 sc.cid,cname,
concat(sum(case when 0<score and score<=60 then 1 else 0 end)/count(1)*100,'%') as '[0-60]',
concat(sum(case when 60<score and score<=70 then 1 else 0 end)/count(1)*100,'%') as '[60-70]',
concat(sum(case when 70<score and score<=85 then 1 else 0 end)/count(1)*100,'%') as '[70-85]',
concat(sum(case when 85<score and score<=100 then 1 else 0 end)/count(1)*100,'%') as '[85-100]'
from sc
left join course
on sc.cid=course.cid
group by cid

查询各科成绩前三名的记录

select 
a.*
from sc a
where 
(select count(1) from sc b where b.cid=a.cid and b.score>a.score)<3
order by cid desc,score desc

查询每门课程被选修的学生数

select cid,count(1)
from sc
group by cid

查询出只选修两门课程的学生学号和姓名

select a.sid,b.sname
from sc a left join student b
on a.sid=b.sid
group by a.sid,b.sname
having count(1)=2

查询男生、女生人数

select ssex,count(1) as counts
from student
GROUP BY ssex

查询名字中含有「风」字的学生信息

select *
from student
where sname like '%风%'

查询同名同性学生名单，并统计同名人数

#提示：自关联
select a.sname,a.ssex,count(1) as conts
from student a inner join student b
on a.sname=b.sname and a.ssex=b.ssex and a.sid!=b.sid
group by a.sname,a.ssex

查询 1990 年出生的学生名单

#使用year函数
select *
from student
where year(sage)=1990

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 avg(score),sid
from sc
group by sid
order by avg(score) desc,sid asc
```

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,b.sname,avg(score)
from sc a inner join student b on a.sid=b.sid 
group by a.sid
having avg(score)>85

查询课程名称为「数学」，且分数低于 60 的学生姓名和分数

select b.score ,sname
from student a right join
(select score,sid from sc a inner join course b on a.cid=b.cid
where  score<60 and cname='数学')b
on b.sid=a.sid

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 sname,cname,score
from student a left join 
(select sid,score,cname
from sc a left join course b
on a.cid=b.cid) b
on a.sid=b.sid

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 sname,cname,score
from 
(select sid,score,cname from sc a left join course b
on a.cid=b.cid) a left join student b
on a.sid=b.sid 
where score>70


select sname,cname,score
from sc a left join course b
on a.cid=b.cid
left join student c
on a.sid=c.sid 
where score>70

查询不及格的课程

select a.*,cname from sc a left join course b
on a.cid=b.cid
where score<60

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 sc.sid,sname
from sc left join student
on sc.sid=student.sid
where cid='01' and score>80

求每门课程的学生人数

select cid, count(1) as counts from sc group by cid;

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 b.*,a.score
from sc a left join student b
on a.sid=b.sid
left join course c
on a.cid=c.cid
left join teacher d
on c.tid=d.tid
where d.tname='张三'
order by a.score desc limit 1

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 s.*
from (
select a.*,
case when @sco = score then @rank
		 when @sco:=score then @rank:=@rank+1 end as rn
from 
(select b.*,score
from sc a left join student b
on a.sid=b.sid
left join course c
on a.cid=c.cid
left join teacher d
on c.tid=d.tid
where d.tname='张三') a,(select @sco:=null,@rank:=0)b)s
where rn=1

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 
a.sid,a.cid
from sc a inner join sc b on a.sid=b.sid
where a.cid!=b.cid and a.score=b.score
group by a.sid,a.cid

查询每门功成绩最好的前两名

select s.cid,s.score,s.sid
from 
(select 
sc.*,
@rank:=if(@c_cid=cid,if(@sco=score,@rank,@rank+1),1) as rank,
@sco:=score,
@c_cid:=cid
from sc,(select @sco:=null,@rank:=0,@c_cid:=null)b
order by cid,score desc)s
where rank<=2

统计每门课程的学生选修人数（超过 5 人的课程才统计）。
```
select cid,count(1)
from sc 
group by cid
having count(1)>5
```

检索至少选修两门课程的学生学号

select sid, count(1) from sc
group by sid
having count(1)>=2

查询选修了全部课程的学生信息

select student.* from sc inner join student
on sc.sid=student.sid
group by sc.sid
having count(1)=(select count(1) from course )

查询各学生的年龄，只按年份来算

#now(),curdate()
select sname,year(now())-year(sage) age from student

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 sname,timestampdiff(year,sage,now())as age from student;
```

查询本周过生日的学生

select *,week(sage),
week(now())
from student where week(sage)=week(now());

查询下周过生日的学生

select *,week(sage),
week(now())
from student where week(sage)=week(now())+1;

查询本月过生日的学生

select *,month(sage),
month(now())
from student where month(sage)=month(now());

查询下月过生日的学生

select *,month(sage),
month(now())
from student where month(sage)=month(now())+1;

MySQL经典45题