17.自主练习

一、建表

1、建库、建表

# 创建数据库

create database mysql_exampleTest;

use mysql_exampleTest;

# 学生表

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)

);

# 课程表

CREATE TABLE Course(

c_id VARCHAR(20),

c_name VARCHAR(20) NOT NULL DEFAULT '',

t_id VARCHAR(20) NOT NULL,

PRIMARY KEY(c_id)

);

# 教师表

CREATE TABLE Teacher(

t_id VARCHAR(20),

t_name VARCHAR(20) NOT NULL DEFAULT '',

PRIMARY KEY(t_id)

);

# 成绩表

CREATE TABLE Score(

s_id VARCHAR(20),

c_id VARCHAR(20),

s_Score INT(3),

PRIMARY KEY(s_id,c_id)

);

2、插入数据：

# 插入学生表测试数据

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' , '1990-05-20' , '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');

Student表：

+------+--------+------------+-------+

| s_id | s_name | s_birth | s_sex |

+------+--------+------------+-------+

| 01 | 赵雷 | 1990-01-01 | 男 |

| 02 | 钱电 | 1990-12-21 | 男 |

| 03 | 孙风 | 1990-05-20 | 男 |

| 04 | 李云 | 1990-08-06 | 男 |

| 05 | 周梅 | 1991-12-01 | 女 |

| 06 | 吴兰 | 1992-03-01 | 女 |

| 07 | 郑竹 | 1989-07-01 | 女 |

| 08 | 王菊 | 1990-01-20 | 女 |

+------+--------+------------+-------+

# 课程表测试数据

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

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

insert into Course values('03' , '英语' , '03');

Course表：

+------+--------+------+

| c_id | c_name | t_id |

+------+--------+------+

| 01 | 语文 | 02 |

| 02 | 数学 | 01 |

| 03 | 英语 | 03 |

+------+--------+------+

# 教师表测试数据

insert into Teacher values('01' , '张三');

insert into Teacher values('02' , '李四');

insert into Teacher values('03' , '王五');

Teacher表：

+------+--------+

| t_id | t_name |

+------+--------+

| 01 | 张三 |

| 02 | 李四 |

| 03 | 王五 |

+------+--------+

# 成绩表测试数据

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);

Score表：

+------+------+---------+

| s_id | c_id | s_Score |

+------+------+---------+

| 01 | 01 | 80 |

| 01 | 02 | 90 |

| 01 | 03 | 99 |

| 02 | 01 | 70 |

| 02 | 02 | 60 |

| 02 | 03 | 80 |

| 03 | 01 | 80 |

| 03 | 02 | 80 |

| 03 | 03 | 80 |

| 04 | 01 | 50 |

| 04 | 02 | 30 |

| 04 | 03 | 20 |

| 05 | 01 | 76 |

| 05 | 02 | 87 |

| 06 | 01 | 31 |

| 06 | 03 | 34 |

| 07 | 02 | 89 |

| 07 | 03 | 98 |

+------+------+---------+

二、实战

?# 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 st.*,sc.s_Score as '语文' ,sc2.s_Score '数学' 
from Student st
left join Score sc on sc.s_id=st.s_id and sc.c_id='01' 
left join Score sc2 on sc2.s_id=st.s_id and sc2.c_id='02'  
where sc.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 st.*,sc.s_Score '语文',sc2.s_Score '数学' 
from Student st
left join Score sc on sc.s_id=st.s_id and sc.c_id='01'
left join Score sc2 on sc2.s_id=st.s_id and sc2.c_id='02'
where sc.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

# 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 st.s_id,st.s_name,(case when ROUND(AVG(sc.s_Score),2) is null then 0 else ROUND(AVG(sc.s_Score)) end ) cjScore 
from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id having AVG(sc.s_Score)<60 or AVG(sc.s_Score) is NULL;

# 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 st.s_id,st.s_name,count(sc.c_id) '选课总数',(case when sum(sc.s_Score) is null or sum(sc.s_Score)='' then 0 else sum(sc.s_Score) end) '总成绩'
from Student st
left outer join Score sc on st.s_id=sc.s_id
group by st.s_id;

?