如何減少mysql查詢中的掃描總數？

Question

我想從下面的查詢中顯示一些有限的記錄，但我應該如何減少在查詢中使用連接執行的掃描的總數並使執行速度更快？

查詢::

select ml.*,m.title as medianame,mt.name as media_type,d.device_name as devicename, 
SUBTIME(ml.end_time,ml.start_time) as playback_duration,d.client_id 
from device_media_log ml left join media m on m.media_id = ml.media_id left join device d on d.device_id = ml.device_id 
left join media_type mt on m.media_type_id = mt.media_type_id 
order by ml.play_date desc,ml.start_time desc,ml.end_time desc; 

所有表包含所需的索引。

Answer 1

我推薦的最好的方法是在可能的地方使用where子句。

select ml。*，m.title as medianame，mt.name as media_type，d.device_name as devicename，SUBTIME（ml.end_time，ml.start_time）as playback_duration，d.client_id from device_media_log ml left join media m on m.media_id = ml.media_id left加入設備d on d.device_id = ml.device_id left join media_type mt on m.media_type_id = mt.media_type_id WHERE SOMETHING = SOMETHING AND SOMETHING = SOMETHING order by ml.play_date desc，ml.start_time desc，ml.end_time desc;