Question

几天前，有人帮我解决了这个问题。我正在尝试获取我的数据库的前10条记录。问题是要点。当我在点数字段上使用SUM时，如果同一个用户有超过1条记录，我会得到实际值的两倍...你知道我做错了什么吗？谢谢

这是只返回用户的第一条记录的代码（不会同一个用户的所有点）

SELECT *
FROM commerce
LEFT JOIN points ON points.id_com = commerce.id
LEFT JOIN comments ON comments.id_com = commerce.id AND (comments.validbycom = 1 AND  comments.validbyus = 1)
LEFT JOIN winners ON winners.id_com = commerce.id
GROUP BY commerce.id
ORDER BY SUM(points) DESC, COUNT(comments.id_com) DESC, commerce.date ASC, COUNT(winners.id_com) DESC LIMIT 10

这是完全返回总数

的两倍的代码

SELECT SUM(points)
    FROM commerce
    LEFT JOIN points ON points.id_com = commerce.id
    LEFT JOIN comments ON comments.id_com = commerce.id AND (comments.validbycom = 1 AND  comments.validbyus = 1)
    LEFT JOIN winners ON winners.id_com = commerce.id
    GROUP BY commerce.id
    ORDER BY SUM(points) DESC, COUNT(comments.id_com) DESC, commerce.date ASC, COUNT(winners.id_com) DESC LIMIT 10

Answer 1

据推测，points列来自points表。额外的join正在引入额外的行。因此，在进行连接之前尝试聚合：

SELECT sumpoints, commerce.id
FROM commerce LEFT JOIN
     (select id_com, sum(points) as sumpoints
      from points
      group by id_com
     ) points
     ON points.id_com = commerce.id LEFT JOIN
     comments
     ON comments.id_com = commerce.id AND (comments.validbycom = 1 AND  comments.validbyus = 1) LEFT JOIN
     winners
     ON winners.id_com = commerce.id
GROUP BY commerce.id
ORDER BY sumpoints DESC, COUNT(comments.id_com) DESC, commerce.date ASC, COUNT(winners.id_com) DESC
LIMIT 10

SUM返回double值

1 个答案: