Question

我有一张表，其中包含演员执行的操作，并希望返回最近的10个操作。我希望演员在这个列表中是独一无二的。 'created'是时间/日期标记。我怎样才能最有效地完成这项工作？我想出了以下查询，其中有效：

SELECT * 
FROM activities a
JOIN 
(SELECT actor, MAX(created) created 
 FROM activities 
 WHERE comment_type <> 'profile.status' 
 GROUP BY actor) t ON (a.actor = t.actor AND a.created = t.created) LIMIT 10

该表最终可能会非常大。

Answer 1

您可以将限制10放在子查询中除此之外看起来还不错

SELECT * FROM activities a
INNER JOIN (
            SELECT 
              actor
              , MAX(created) created 
            FROM activities 
            WHERE comment_type <> 'profile.status' 
            GROUP BY actor
            LIMIT 10 OFFSET 0) t
      ON (a.actor = t.actor AND a.created = t.created) LIMIT 10

Answer 2

如果你只需要演员，你可以这样做

SELECT DISTINCT actor -- and any other actor specific columns that are unique to the actor
FROM activities 
WHERE comment_type <> 'profile.status'
ORDER BY Created DESC
LIMIT 10

SQL：返回最近的操作，但限制为10个结果

2 个答案: