mysql - 需要帮助通过连接优化 MYSQL 查询

Question

我正在“收藏夹”表(300 万行)和“项目”表(60 万行)之间进行连接。查询耗时从 0.3 秒到 2 秒不等，我希望可以对其进行一些优化。

Favorites.faver_profile_id 和 Items.id 已编入索引。我没有使用 faver_profile_id 索引，而是在 (faver_profile_id,id) 上创建了一个新索引，它消除了按 id 排序时所需的文件排序。不幸的是，这个索引根本没有帮助，我可能会删除它(是的，还有 3 个小时的停机时间来删除索引..)

关于如何优化此查询的任何想法？

如果有帮助:
Favorite.removed 和 Item.removed 在 98% 的时间里都是“0”。
大约 80% 的时间 Favorite.collection_id 为 NULL。

SELECT `Item`.`id`, `Item`.`source_image`, `Item`.`cached_image`, `Item`.`source_title`, `Item`.`source_url`, `Item`.`width`, `Item`.`height`, `Item`.`fave_count`, `Item`.`created`        
FROM `favorites` AS `Favorite`
LEFT JOIN `items` AS `Item` 
ON (`Item`.`removed` = 0 AND `Favorite`.`notice_id` = `Item`.`id`) 
WHERE ((`faver_profile_id` = 1) AND (`collection_id` IS NULL) AND (`Favorite`.`removed` = 0) AND (`Item`.`removed` = '0')) 
ORDER BY `Favorite`.`id` desc LIMIT 50;

+----+-------------+----------+--------+----------------------------------------------------- ----------+------------------+---------+-----------------------------------------+------+-------------+
| id | select_type | table    | type   | possible_keys                                                 | key              | key_len | ref                                     | rows | Extra       |
+----+-------------+----------+--------+---------------------------------------------------------------+------------------+---------+-----------------------------------------+------+-------------+
|  1 | SIMPLE      | Favorite | ref    | notice_id,faver_profile_id,collection_id_idx,idx_faver_idx_id | idx_faver_idx_id |       4 | const                                   | 7910 | Using where |
|  1 | SIMPLE      | Item     | eq_ref | PRIMARY                                                       | PRIMARY          |       4 | gragland_imgfavebeta.Favorite.notice_id |    1 | Using where |
+----+-------------+----------+--------+---------------------------------------------------------------+------------------+---------+-----------------------------------------+------+-------------+

+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| favorites | CREATE TABLE `favorites` (
             `id` int(11) NOT NULL auto_increment COMMENT 'unique identifier',
             `faver_profile_id` int(11) NOT NULL default '0',
             `collection_id` int(11) default NULL,
             `collection_order` int(8) default NULL,
             `created` datetime NOT NULL default '0000-00-00 00:00:00' COMMENT 'date this record was created',
             `modified` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP COMMENT 'date this record was modified',
             `notice_id` int(11) NOT NULL default '0',
             `removed` tinyint(1) NOT NULL default '0',
              PRIMARY KEY  (`id`),
              KEY `notice_id` (`notice_id`),
              KEY `faver_profile_id` (`faver_profile_id`),
              KEY `collection_id_idx` (`collection_id`),
              KEY `idx_faver_idx_id` (`faver_profile_id`,`id`)
              ) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+


+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| items |CREATE TABLE `items` (
         `id` int(11) NOT NULL auto_increment COMMENT 'unique identifier',
         `submitter_id` int(11) NOT NULL default '0' COMMENT 'who made the update',
         `source_image` varchar(255) default NULL COMMENT 'update content',
         `cached_image` varchar(255) default NULL,
         `source_title` varchar(255) NOT NULL default '',
         `source_url` text NOT NULL,
         `width` int(4) NOT NULL default '0',
         `height` int(4) NOT NULL default '0',
         `status` varchar(122) NOT NULL default '',
         `popular` int(1) NOT NULL default '0',
         `made_popular` timestamp NULL default NULL,
         `fave_count` int(9) NOT NULL default '0',
         `tags` text,
         `user_art` tinyint(1) NOT NULL default '0',
         `nudity` tinyint(1) NOT NULL default '0',
         `created` datetime NOT NULL default '0000-00-00 00:00:00' COMMENT 'date this record was created',
         `modified` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP COMMENT 'date this record was modified',
         `removed` int(1) NOT NULL default '0',
         `nofront` tinyint(1) NOT NULL default '0',
         `test` varchar(10) NOT NULL default '',
         `recs` text,
         `recs_data` text,
         PRIMARY KEY  (`id`),
         KEY `notice_profile_id_idx` (`submitter_id`),
         KEY `content` (`source_image`),
         KEY `idx_popular` (`popular`),
         KEY `idx_madepopular` (`made_popular`),
         KEY `idx_favecount_idx_id` (`fave_count`,`id`)
         ) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Answer 1

首先，您按 favorites.id 排序，它是 favorites 表中的聚簇主键。这不是必需的，因为您将加入 favorites 到 items 而不是 items 到 favorites。

其次，WHERE中的(Item.removed = '0')是多余的，因为JOIN中已经使用了相同的条件。

第三，将join中的条件顺序改为:

`Favorite`.`notice_id` = `Item`.`id` AND `Item`.`removed` = 0

优化器将能够使用您的主键作为索引。您甚至可以考虑在 items 表上创建 (id, removed) 索引。

接下来，在 faverites 中创建 (faver_profile_id, removed) 索引(或者最好更新 faver_profile_id 索引)并将 WHERE 中的条件顺序更改为以下内容:

(`faver_profile_id` = 1)
AND (`Favorite`.`removed` = 0)
AND (`collection_id` IS NULL)

UPD:对不起，我错过了您已经将收藏夹加入项目。那么就不需要 ORDER BY 了。你应该得到如下结果:

SELECT
    `Item`.`id`,
    `Item`.`source_image`,
    `Item`.`cached_image`,
    `Item`.`source_title`,
    `Item`.`source_url`, 
    `Item`.`width`,
    `Item`.`height`,
    `Item`.`fave_count`,
    `Item`.`created`        
FROM `favorites` AS `Favorite`
LEFT JOIN `items` AS `Item` 
ON (`Favorite`.`notice_id` = `Item`.`id` AND `Item`.`removed` = 0) 
WHERE `faver_profile_id` = 1
    AND `Favorite`.`removed` = 0
    AND `collection_id` IS NULL
LIMIT 50;

还有一件事，当你有 KEY idx_faver_idx_id (faver_profile_id,id) 你不需要 KEY faver_profile_id (faver_profile_id)，因为第二个索引只是复制了 idx_faver_idx_id 的一半。我希望您能按照我的建议扩展第二个索引。