sql - 有没有更快的方法来计算连接上的记录

Question

当配置文件是 Actor 时，此查询会为我提供证据记录最多的配置文件。 有什么方法可以让它在 mysql 查询中更快？

SELECT profiles.*, count(*) AS counted_profiles 
FROM `profiles` 
INNER JOIN (SELECT ev.actor_id 
            FROM evidences AS ev 
            WHERE ev.actor_type = 'Profile') AS ev2
ON ev2.actor_id = profiles.id 
GROUP BY ev2.actor_id 
ORDER BY counted_profiles DESC LIMIT 10

Answer 1

您可以删除 profiles.*，删除子选择，并为连接字段添加索引。

另外，考虑一下:

SELECT ev.actor_id, count(*) AS counted_profiles 
FROM `profiles` INNER JOIN evidences AS ev
      ON ev.actor_id = profiles.id AND ev.actor_type = 'Profile'
GROUP BY ev.actor_id 
ORDER BY counted_profiles DESC LIMIT 10