mysql 行转列，对列的分组求和，对行求和

Posted 2021-11-26 mryangbo

 

CREATE TABLE students(
　　id INT PRIMARY KEY,
　　NAME VARCHAR(11)
);

CREATE TABLE courses(
　　id INT PRIMARY KEY,
　　NAME VARCHAR(11)
);

 

CREATE TABLE scores(
　　sid INT,
　　cid INT,
　　score INT,
　　RIMARY KEY (sid,cid)
);

 3表关联查询：

SELECT st.id,st.name,c.NAME course,sc.score FROM students st
LEFT JOIN scores sc ON st.id=sc.sid
LEFT JOIN courses c ON sc.cid=c.id

将课程分类转为列名，其列值为分数：

SELECT t.id,t.name,
CASE course WHEN ‘语文‘ THEN score ELSE 0 END a,
CASE course WHEN ‘数学‘ THEN score ELSE 0 END b,
CASE course WHEN ‘英语‘ THEN score ELSE 0 END c,
CASE course WHEN ‘历史‘ THEN score ELSE 0 END d

FROM

(SELECT st.id,st.name,c.NAME course,sc.score FROM students st
LEFT JOIN scores sc ON st.id=sc.sid
LEFT JOIN courses c ON sc.cid=c.id) t

 

对上表按人员id分组，并将分完组的个列分数相加，组合到一行中，并对行求和：

SELECT t2.id,t2.name,SUM(a) ‘语文‘,SUM(b) ‘数学‘,SUM(c) ‘英语‘,SUM(d) ‘历史‘,SUM(a+b+c+d) ‘总分‘ FROM
(
　　SELECT t.id,t.name,
　　CASE course WHEN ‘语文‘ THEN score ELSE 0 END a,
　　CASE course WHEN ‘数学‘ THEN score ELSE 0 END b,
　　CASE course WHEN ‘英语‘ THEN score ELSE 0 END c,
　　CASE course WHEN ‘历史‘ THEN score ELSE 0 END d

　　FROM

　　　　(SELECT st.id,st.name,c.NAME course,sc.score FROM students st
　　　　LEFT JOIN scores sc ON st.id=sc.sid
　　　　LEFT JOIN courses c ON sc.cid=c.id) t

) t2
GROUP BY t2.id;