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  • mysql 行转列,对列的分组求和,对行求和

    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;

     

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  • 原文地址:https://www.cnblogs.com/mryangbo/p/10798459.html
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