优化sql查询使用索引或重写sql

Question

我有sql查询

SELECT 
  bd2.*, 
  bdmax.last_video, 
  bdmax.number_videos 
FROM 
  video bd2 
  JOIN 
    ( SELECT 
      bd.video_cat_id, 
      MAX(bd.last_poster_time) AS last_video, 
      COUNT(bd.video_id) as number_videos 
    FROM 
      video bd 
    GROUP BY 
      bd.video_cat_id 
    ) AS bdmax 
    ON bd2.video_cat_id = bdmax.video_cat_id 
      AND bd2.last_poster_time = bdmax.last_video;

表格键是

  PRIMARY KEY (`video_id`),
  KEY `video_cat_id` (`video_cat_id`),
  KEY `video_user_id` (`video_user_id`),
  KEY `video_time` (`video_time`),
  KEY `video_urn` (`video_urn`),
  KEY `last_poster_time` (`last_poster_time`),
  KEY `video_username` (`video_username`),
  KEY `video_approval` (`video_approval`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin AUTO_INCREMENT=45619 ;

如何优化此查询以使用索引？

Answer 1

不要将表名放在列名的开头，从而造成混乱。然后这个'复合'索引

INDEX(cat_id, last_poster_time, id)

将有助于子查询（通过“覆盖”）和JOIN。

这个查询的一部分是“groupwise max”。但是COUNT 意味着对最大值的优化没有用。