MySQL查询 - 跨多个表的多个总和，需要忽略空值

Question

我正在尝试从 5 个不同的表中对 thumbsup 减去 thumbsdown 进行以下 SUM，然后将所有这些值加在一起，如果所有“commthumbs”都返回一行，但如果一个或多个“commthumbs”有没有行然后它返回一个空值。我尝试使用 IFNULL，如下面的第一个 LEFT JOIN 所示。我也尝试过 ISNULL 和 COALESCE 代替 IFNULL 但似乎仍然无法让它工作。关于我做错了什么有什么建议吗？

    SELECT 
        user.userID, user.username,
        SUM(a.commthumbs+b.commthumbs+c.commthumbs+d.commthumbs) AS 'commthumbs', 
        e.fixthumbs AS 'fixthumbs'
    FROM
        user

    LEFT JOIN (
        SELECT 
        userID, IFNULL(SUM(gameCommThUp-gameCommThDown),0) AS 'commthumbs'
        FROM
        gamecomm
        GROUP BY userID) a ON a.userID = user.userID

    LEFT JOIN (
        SELECT 
        userID, SUM(fixCommThUp-fixCommThDown) AS 'commthumbs'
        FROM 
        fixcomm
        GROUP BY userID) b ON b.userID = user.userID

    LEFT JOIN (
        SELECT 
        userID, SUM(replyCommThUp-replyCommThDown) AS 'commthumbs'
        FROM gamereply
        GROUP BY userID) c ON c.userID = user.userID

    LEFT JOIN (
        SELECT userID, SUM(fixReplyThUp-fixReplyThDown) AS 'commthumbs'
        FROM fixreply
        GROUP BY userID) d ON d.userID = user.userID

    LEFT JOIN (
        SELECT 
        userID, SUM(fixThUp-fixThDown) AS 'fixthumbs'
        FROM 
        fix
        GROUP BY userID) e ON e.userID = user.userID

    WHERE user.userID = 2;

Answer 1

试试这个

  SELECT 
        user.userID, user.username,
        SUM(IFNULL(a.commthumbs,0)+IFNULL(b.commthumbs,0)+IFNULL(c.commthumbs,0)+IFNULL(d.commthumbs,0)) AS 'commthumbs', 
        IFNULL(e.fixthumbs,0) AS 'fixthumbs'
    FROM
        user

    LEFT JOIN (
        SELECT 
        userID, SUM(IFNULL(gameCommThUp,0)-IFNULL(gameCommThDown,0)) AS 'commthumbs'
        FROM
        gamecomm
        GROUP BY userID) a ON a.userID = user.userID

    LEFT JOIN (
        SELECT 
        userID, SUM(IFNULL(fixCommThUp,0)-IFNULL(fixCommThDown,0)) AS 'commthumbs'
        FROM 
        fixcomm
        GROUP BY userID) b ON b.userID = user.userID

    LEFT JOIN (
        SELECT 
        userID, SUM(IFNULL(replyCommThUp,0)-IFNULL(replyCommThDown,0)) AS 'commthumbs'
        FROM gamereply
        GROUP BY userID) c ON c.userID = user.userID

    LEFT JOIN (
        SELECT userID, SUM(IFNULL(fixReplyThUp,0)-IFNULL(fixReplyThDown,0)) AS 'commthumbs'
        FROM fixreply
        GROUP BY userID) d ON d.userID = user.userID

    LEFT JOIN (
        SELECT 
        userID, SUM(IFNULL(fixThUp,0)-IFNULL(fixThDown,0)) AS 'fixthumbs'
        FROM 
        fix
        GROUP BY userID) e ON e.userID = user.userID

    WHERE user.userID = 2;