建表

CREATE TABLE `Student`(
    `s_id` VARCHAR(20),
    `s_name` VARCHAR(20) NOT NULL DEFAULT '',
    `s_birth` VARCHAR(20) NOT NULL DEFAULT '',
    `s_sex` VARCHAR(10) NOT NULL DEFAULT '',
    PRIMARY KEY(`s_id`)
);
CREATE TABLE `Course`(
    `c_id`  VARCHAR(20),
    `c_name` VARCHAR(20) NOT NULL DEFAULT '',
    `t_id` VARCHAR(20) NOT NULL,
    PRIMARY KEY(`c_id`)
);
CREATE TABLE `Teacher`(
    `t_id` VARCHAR(20),
    `t_name` VARCHAR(20) NOT NULL DEFAULT '',
    PRIMARY KEY(`t_id`)
);
CREATE TABLE `Score`(
    `s_id` VARCHAR(20),
    `c_id`  VARCHAR(20),
    `s_score` INT(3),
    PRIMARY KEY(`s_id`,`c_id`)
);
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('08' , '王菊' , '1990-01-20' , '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 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);

student

Course

Teacher

Score

题目：

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 s.*,sc1.s_score AS '01',sc2.s_score AS '02'
from Student as s 
    join  Score as sc1 
    on s.s_id=sc1.s_id and sc1.c_id=01
    join  Score as sc2 
    on s.s_id=sc2.s_id and sc2.c_id=02
    join Course as c
    on c.c_id=sc1.c_id
where sc1.s_score>sc2.s_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 s.*,sc1.s_score as '01',sc2.s_score as '02'
from Student as s 
    join Score as sc1 
        on s.s_id=sc1.s_id and sc1.c_id=01
    join Score as sc2
        on s.s_id=sc2.s_id and sc2.c_id=02
where sc1.s_score<sc2.s_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 s.s_id,s.s_name,avg(sc.s_score) as avg
from Student as s 
    join Score as sc 
        on s.s_id=sc.s_id 
group by sc.s_id having avg(sc.s_score)>=60

tips：

avg保留几位小数

round(avg(___),2)

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

    -- (包括有成绩的和无成绩的) 

select s.s_id,s.s_name,round(avg(sc.s_score),2) as avg
from Student as s 
    join Score as sc 
        on s.s_id=sc.s_id 
group by sc.s_id having avg(sc.s_score)<60

有问题！
08没成绩

select s.s_id,s.s_name,round(avg(sc.s_score),2) as avg
from Student as s 
right     join Score as sc 
        on s.s_id=sc.s_id 
group by s.s_id having avg(sc.s_score)<60
UNION
SELECT s.s_id,s.s_name,0 as avg 
from Student as s
where s.s_id not in (select s_id from 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 s.s_id,s.s_name,count(sc.c_id) as count,sum(sc.s_score) as sum
from Student as s 
left join Score as sc 
        on s.s_id=sc.s_id 
group by s.s_id

6.查询‘李’姓老师的数量

select count(t.t_id)
from Teacher t
where t_name like '李%'

7.查询学过’张三‘老师授课的同学的信息

select s.*
from Student as s 
left join Score as sc 
    on s.s_id=sc.s_id
left join Course as c
    on sc.c_id=c.c_id
left join Teacher as t 
    on c.t_id=t.t_id
where t.t_name ='张三'

8.查询没学过”张三”老师授课的同学的信息

select s.*
from Student as s
where s.s_id not in 
(
SELECT s.s_id
from Student as s 
left join Score as sc 
    on s.s_id=sc.s_id
left join Course as c
    on sc.c_id=c.c_id
left join Teacher as t 
    on c.t_id=t.t_id
where t.t_name = '张三'
)

9.查询学过01也学过02的课程的同学的信息

select s.*
from Student as s 
    join Score as sc1 
        on s.s_id=sc1.s_id and sc1.c_id=01
    join Score as sc2
        on s.s_id=sc2.s_id and sc2.c_id=02

10.查询学过01但是没有学过02的同学的信息

select s.*
from Student as s 
    join Score as sc1 
        on s.s_id=sc1.s_id and sc1.c_id=01
where s.s_id not in (select s_id from Score where c_id=02)

11.查询没有学全所有课程的同学的信息

select s.* from Student s
where s.s_id not in 
(
select s.s_id
from Student as s 
    join Score as sc1 
        on s.s_id=sc1.s_id and sc1.c_id=01
join Score as sc2 
        on s.s_id=sc2.s_id and sc2.c_id=02
join Score as sc3 
        on s.s_id=sc3.s_id and sc3.c_id=03
)

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 s.*
from Student s
join Score sc 
on s.s_id=sc.s_id
where sc.c_id in (select c_id from Score where s_id=01)
AND s.s_id <>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

完全相同

    SELECT s.* FROM Student as s
 WHERE s.s_id IN(
        SELECT sc1.s_id FROM Score sc1 
        LEFT JOIN (SELECT DISTINCT c_id FROM Score WHERE s_id=01) sc2 ON sc1.c_id=sc2.c_id
        WHERE sc1.s_id<>01
        GROUP BY sc1.s_id
        HAVING COUNT(sc1.c_id)=(SELECT DISTINCT COUNT(c_id) FROM Score WHERE s_id=01) AND COUNT(sc2.c_id)=COUNT(sc1.c_id)    -- 自身课程数=01课程数，且，自身课程=01课程
    );

14.查询没学过‘张三’老师教的任一门课程的学生姓名

select distinct s.s_name
from Student s
where s.s_name not in 
(select distinct s.s_name
from Student s
join Score sc
    on s.s_id=sc.s_id
join Course c
    on sc.c_id=c.c_id
join Teacher t
    on c.t_id=t.t_id
where t.t_name ='张三')

15.查询两门及以上不及格课程的同学的学号姓名及平均成绩

select s.s_name,avg(sc.s_score) as avg 
from Student as s
    join Score as sc 
on s.s_id=sc.s_id
where s.s_id in 
(select s_id from Score sc
where s_score<60
group by sc.s_id
HAVING count(*)>=2
)
group by sc.s_id

16.检索01分数小于60，按分数降序排列的学生信息

select s.*
from Student as s
    join Score as sc 
on s.s_id=sc.s_id 
where sc.c_id=01
and sc.s_score<60
order by sc.s_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

select sc.*,avg 
from Score sc
join (select s_id,avg(s_score) as avg from Score group by s_id) sc2
on sc.s_id=sc2.s_id 
order by avg desc

*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

SELECT sc.c_id,c.c_name,max(sc.s_score),min(sc.s_score),avg(sc.s_score) as avg,
SUM(CASE WHEN sc.s_score <=60 THEN 1 ELSE 0 END)/ COUNT( sc.s_id) as '及格率',
SUM(CASE WHEN sc.s_score BETWEEN 70 AND 80 THEN 1 ELSE 0 END)/ COUNT(s_id) as'中等率',    
SUM(CASE WHEN sc.s_score BETWEEN 80 AND 90 THEN 1 ELSE 0 END)/ COUNT( s_id) as'优良率',
SUM(CASE WHEN sc.s_score >=90 THEN 1 ELSE 0 END)/ COUNT( sc.s_id)/ COUNT(s_id) as'优秀率'
FROM Score sc
JOIN Course c
        on sc.c_id=c.c_id
group by sc.c_id

19.按各科成绩进行排序，并显示排名

set @rank:=0;
set @prerank:=null;
set @intrank:=1;
select s_id,s_score,c_id,rank
from(
SELECT s_id,s_score,c_id,@rank:=if(@prerank=s_score,@rank,@intrank)as rank,
@intrank:=@intrank+1,
@prerank:=s_score
from Score
order by c_id,s_score desc) r

20.查询学生的总成绩并进行排名

set @rank:=0;
set @prerank:=null;
set @intrank:=1;
select s_id,s_score,sum,rank
from(
SELECT s_id,s_score,sum(s_score) as 'sum',@rank:=if(@prerank=sum(s_score),@rank,@intrank)as rank,
@intrank:=@intrank+1,
@prerank:=sum(s_score)
from Score
group by s_id
order by sum(s_score) desc) r

21.查询不同老师所教不同课程平均分从高到低显示

SELECT t_name,t.t_id,avg(s_score) as avg
from Teacher t
    join Course c
    on t.t_id=c.t_id
    join Score s
    on c.c_id=s.c_id
group by s.c_id 
order by avg(s_score) desc