php - 长 SQL 查询优化

Question

当有很多人登录该站点时，我有一个 sql 查询会关闭我的整个服务器。

我花了一整天的时间试图找出如何通过索引教程修复它，但我仍然不明白我该如何修复这个查询，或者我是否完全可以

这是查询:

SELECT t.id, 
       t.title, 
       t.s_secret, 
       t.content, 
       t.senton, 
       t.hidden, 
       t.reported, 
       t.root_id, 
       t.sender_id, 
       t.s_contact_name, 
       t.s_contact_email, 
       t.item_id, 
       t.status_id, 
       t.event_id, 
       l.id              AS last_id, 
       l.title           AS last_title, 
       l.s_secret        AS last_s_secret, 
       l.content         AS last_content, 
       l.senton          AS last_sentOn, 
       l.hidden          AS last_hidden, 
       l.reported        AS last_reported, 
       l.root_id         AS last_root_id, 
       l.sender_id       AS last_sender_id, 
       l.s_contact_name  AS last_s_contact_name, 
       l.s_contact_email AS last_s_contact_email, 
       l.item_id         AS last_item_id, 
       l.status_id       AS last_status_id, 
       l.event_id        AS last_event_id, 
       last.count        AS t_count 
FROM   oc_t_mmessenger_recipients r 
       JOIN oc_t_mmessenger_message l 
         ON l.id = r.message_id 
       JOIN (SELECT Max(im.id) AS max, 
                    Count(1)   AS count 
             FROM   oc_t_mmessenger_message im 
             GROUP  BY root_id) last 
         ON r.message_id = last.max 
       JOIN oc_t_mmessenger_message t 
         ON t.id = l.root_id 
       JOIN oc_t_mmessenger_message_labels ml 
         ON ( ml.fk_i_message_id = t.id 
              AND ml.fk_i_label_id = 1 
              AND ml.fk_i_user_id = 2569 ) 
WHERE  ( r.recipient_id = 2469 
          OR l.sender_id = 2469 ) 
ORDER  BY last.max DESC 
LIMIT  0, 10 

如果我通过 phpmyadmin 为像 recipient_id 和 sender_id 这样的表创建索引，它会有帮助吗？ 任何提示将不胜感激! 谢谢。

编辑:

这是当前表的索引:

Answer 1

您可能希望将查询拆分为两个而不是 OR 语句。 喜欢:

(SELECT 
# everything from your query
WHERE r.recipient_id = 2469)
UNION
(SELECT
# everything from your query, again
WHERE l.sender_id = 2469)

这样您应该能够同时使用 recipient_id 和 sender_id 索引。

但正如其他人所说，最大的问题可能是内部选择。