如何加快MySQL查询速度？

Question

有人可以帮我解决这个问题吗？它工作正常，但需要花费太多时间。我确定问题是tb_activities中的OR语句过多。有没有人有任何想法让这个查询更快？

SELECT tb_posts.*
FROM   tb_posts
WHERE  EXISTS (SELECT c_id
               FROM   tb_users
               WHERE  tb_posts.c_uid = tb_users.c_id
                      AND tb_users.c_tokens > 0)
       AND NOT EXISTS (SELECT c_id
                       FROM   tb_activities
                       WHERE  tb_posts.c_url = tb_activities.c_url
                              AND tb_activities.c_category = 'gplus'
                              AND ( tb_activities.c_uid LIKE '%,6x1,%'
                                     OR tb_activities.c_uid LIKE '%,6x1'
                                     OR tb_activities.c_uid LIKE '6x1,%'
                                     OR tb_activities.c_uid = '6x1' ))
       AND NOT EXISTS (SELECT c_id
                       FROM   tb_blacklist
                       WHERE  tb_posts.c_url LIKE Concat('%', tb_blacklist.c_url
                                                  , '%')
                              AND tb_blacklist.c_times > 2
                              AND tb_blacklist.c_category = 'gplus')
       AND tb_posts.c_category = 'classic'
       AND tb_posts.c_status = 'run'
       AND tb_posts.c_nogplus = 0
GROUP  BY tb_posts.c_url
ORDER  BY tb_posts.c_cost DESC,
          tb_posts.c_date DESC
LIMIT  30  

Answer 1

我在这里做的是重写第一个WHERE EXISTS ...。为什么？ Here就是答案。另一个有趣的读物是this。因此，您可以考虑进一步重写查询。不幸的是我现在没有时间了。但是，通过添加（复合）索引，您将获得主要性能提升 。将索引放在JOIN所基于的列或WHERE子句中经常使用的列上。

SELECT tb_posts.*
FROM   tb_posts
INNER JOIN tb_users ON tb_posts.c_uid = tb_users.c_id
WHERE  tb_users.c_tokens > 0
       AND NOT EXISTS (SELECT c_id
                       FROM   tb_activities
                       WHERE  tb_posts.c_url = tb_activities.c_url
                              AND tb_activities.c_category = 'gplus'
                              AND ( tb_activities.c_uid LIKE '%,6x1,%'
                                     OR tb_activities.c_uid LIKE '%,6x1'
                                     OR tb_activities.c_uid LIKE '6x1,%'
                                     OR tb_activities.c_uid = '6x1' ))
       AND NOT EXISTS (SELECT c_id
                       FROM   tb_blacklist
                       WHERE  tb_posts.c_url LIKE Concat('%', tb_blacklist.c_url, '%')
                              AND tb_blacklist.c_times > 2
                              AND tb_blacklist.c_category = 'gplus')
       AND tb_posts.c_category = 'classic'
       AND tb_posts.c_status = 'run'
       AND tb_posts.c_nogplus = 0
GROUP  BY tb_posts.c_url
ORDER  BY tb_posts.c_cost DESC,
          tb_posts.c_date DESC
LIMIT  30

您也可以阅读EXPLAIN，以便了解使用（或未使用）哪些索引。

作为旁注，Peter Kiss关于改变WHERE条款顺序的提示是无稽之谈。查询优化器无论如何都会处理它。