在分组之前寻找更有效的方式与联盟

下面的代码适用于我在寻找的内容，但我试图查看是否有更好的方法来创建高效的新闻Feed。这个新闻源应该选择最近的评论和/或喜欢等，但只显示最近的每个用户（即如果John喜欢2个项目并评论3个项目，只显示最近的评论和喜欢。在涉及多种的UNION在分组之前寻找更有效的方式与联盟

SELECT * 
FROM (SELECT username, time, comment FROM comments ORDER BY time DESC) AS temp 
GROUP by username 
UNION 
SELECT * 
FROM (SELECT username, time, likes FROM likes ORDER BY time DESC) AS temp 
GROUP BY username 
ORDER BY time DESC 
LIMIT 10

来源

2013-02-16 Kevin

我认为你可以JOIN上username两个表，但是这会给你额外的列，而不是工会，像：

SELECT 
    c1.username, 
    c1.`time` AS CommentTime, 
    c1.comment, 
    l1.`time` AS LikeTime, 
    l1.likes 
FROM comments AS c1 
INNER JOIN 
(
    SELECT username, MAX(`time`) LatestTime 
    FROM Comments 
    GROUP BY username 
) AS c2 ON c1.username = c2.username 
     AND c1.`time` = c2.LatestTime 
INNER JOIN Likes l1 ON c1.username = l2.username 
INNER JOIN 
(
    SELECT username, MAX(`time`) LatestTime 
    FROM Likes 
    GROUP BY username 
) AS l2 ON l1.username = l2.username 
     AND l1.`time` = l2.latestTime 
ORDER BY c1.`time` DESC 
LIMIT 10;

这会给你带最新评论的username和最新的likes最新的时间。

来源

2013-02-16 09:28:41

在分组之前寻找更有效的方式与联盟

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