Mysql 在类别中搜索时如何优化联接
我有一张桌子,上面有一些物品:Mysql 在类别中搜索时如何优化联接,mysql,categories,Mysql,Categories,我有一张桌子,上面有一些物品: CREATE TABLE `ost_content` ( `uid` mediumint(8) unsigned NOT NULL AUTO_INCREMENT, `type` enum('media','serial','season','series') NOT NULL, `alias` varchar(200) NOT NULL, `views` mediumint(7) NOT NULL DEFAULT '0', `ratings_c
CREATE TABLE `ost_content` (
`uid` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
`type` enum('media','serial','season','series') NOT NULL,
`alias` varchar(200) NOT NULL,
`views` mediumint(7) NOT NULL DEFAULT '0',
`ratings_count` enum('0','1','2','4','5') NOT NULL DEFAULT '0',
`ratings_sum` mediumint(5) NOT NULL DEFAULT '0',
`upload_date` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`conversion_status` enum('converting','error','success','announcement') NOT NULL DEFAULT 'converting',
PRIMARY KEY (`uid`),
UNIQUE KEY `idx_uid_type` (`uid`,`type`),
KEY `idx_type` (`type`),
KEY `idx_upload_date DESC` (`upload_date`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
和表,用于连接具有类别的项目:
CREATE TABLE `ost_categories2media` (
`categories2media_id` mediumint(6) unsigned NOT NULL AUTO_INCREMENT,
`categories2media_category_id` smallint(5) unsigned NOT NULL,
`categories2media_uid` mediumint(8) unsigned NOT NULL,
PRIMARY KEY (`categories2media_id`),
KEY `categories2media_media_id` (`categories2media_uid`),
KEY `categories2media_category_id` (`categories2media_category_id`)
) ENGINE=InnoDB AUTO_INCREMENT=501114 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
然后,我执行查询:
SELECT
c1.uid,
c1.alias,
c1.type,
c1.views,
c1.upload_date,
c1.ratings_sum,
c1.ratings_count,
c1.conversion_status
FROM
ost_content c1
LEFT JOIN ost_categories2media c2m ON c2m.categories2media_uid = c1.uid
WHERE
c2m.categories2media_category_id = '53'
AND c1.conversion_status IN ('success', 'announcement')
AND c1.type IN ('serial', 'media')
ORDER BY
c1.upload_date DESC
LIMIT 16, 16
它执行速度慢,分类2媒体分类id检查多行:
+----+-------------+-------+--------+--------------------------------------------------------+------------------------------+---------+---------------------------------+-------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+--------------------------------------------------------+------------------------------+---------+---------------------------------+-------+----------------------------------------------+
| 1 | SIMPLE | c2m | ref | categories2media_media_id,categories2media_category_id | categories2media_category_id | 2 | const | 32076 | Using where; Using temporary; Using filesort |
| 1 | SIMPLE | c1 | eq_ref | PRIMARY,idx_uid_type,idx_type | PRIMARY | 3 | uakino.c2m.categories2media_uid | 1 | Using where |
+----+-------------+-------+--------+--------------------------------------------------------+------------------------------+---------+---------------------------------+-------+----------------------------------------------+
如何优化或重写此查询?Mysql索引就像厨师一样,太多的索引不是很有用,因为Mysql每个表只使用一个索引。让我们看一下ost_Categories2媒体, 这是三列上的三个独立索引。您最好使用这样的两个索引
PRIMARY KEY (`categories2media_id`),
KEY `categories2media_media_id` (`categories2media_uid`,`categories2media_category_id`)
现在,mysql不再需要在categories2media\u uid
或categories2media\u category\u id
上的索引之间做出选择,它有一个涵盖这两个方面的索引
查看您的ost_内容表,我们看到
PRIMARY KEY (`uid`),
UNIQUE KEY `idx_uid_type` (`uid`,`type`),
KEY `idx_type` (`type`),
KEY `idx_upload_date DESC` (`upload_date`)
有些索引有点多余。在uid
字段上筛选的任何查询都可以使用PK,而在type
上筛选的任何查询都可以使用idx\u type
,这意味着idx\u uid\u type
仅用于强制唯一性。但我们可以这样使它更有用:
PRIMARY KEY (`uid`),
UNIQUE KEY `idx_uid_type` (`type`,`uid`),
KEY `idx_upload_date DESC` (`upload_date`)
我们去掉了一个索引!这应该会让你的索引速度更快。您仍然有一个关于上载日期的索引,该索引未在这个特殊查询中使用。那么,综合指数呢
PRIMARY KEY (`uid`),
UNIQUE KEY `idx_uid_type` (`type`,`uid`),
KEY `idx_upload_date DESC` (`uid`,`upload_date`)
Mysql索引就像厨师,太多的索引不是很有用,因为Mysql每个表只使用一个索引。让我们看一下ost_Categories2媒体, 这是三列上的三个独立索引。您最好使用这样的两个索引
PRIMARY KEY (`categories2media_id`),
KEY `categories2media_media_id` (`categories2media_uid`,`categories2media_category_id`)
现在,mysql不再需要在categories2media\u uid
或categories2media\u category\u id
上的索引之间做出选择,它有一个涵盖这两个方面的索引
查看您的ost_内容表,我们看到
PRIMARY KEY (`uid`),
UNIQUE KEY `idx_uid_type` (`uid`,`type`),
KEY `idx_type` (`type`),
KEY `idx_upload_date DESC` (`upload_date`)
有些索引有点多余。在uid
字段上筛选的任何查询都可以使用PK,而在type
上筛选的任何查询都可以使用idx\u type
,这意味着idx\u uid\u type
仅用于强制唯一性。但我们可以这样使它更有用:
PRIMARY KEY (`uid`),
UNIQUE KEY `idx_uid_type` (`type`,`uid`),
KEY `idx_upload_date DESC` (`upload_date`)
我们去掉了一个索引!这应该会让你的索引速度更快。您仍然有一个关于上载日期的索引,该索引未在这个特殊查询中使用。那么,综合指数呢
PRIMARY KEY (`uid`),
UNIQUE KEY `idx_uid_type` (`type`,`uid`),
KEY `idx_upload_date DESC` (`uid`,`upload_date`)
首先,
左连接是不必要的。因此,您可以将查询编写为:
SELECT c.*
FROM ost_content c JOIN
ost_categories2media c2m
ON c2m.categories2media_uid = c.uid
WHERE c2m.categories2media_category_id = '53' AND
c.conversion_status IN ('success', 'announcement') AND
c.type IN ('serial', 'media')
ORDER BY c.upload_date DESC
LIMIT 16, 16;
不幸的是,内容表上的条件不是简单的=
条件。如果是,建议使用ost\u内容(转换状态、类型、uid)
索引。这可能仍然是更好的选择
另一种选择是另一种方式:在ost\u categories2media(categories2media\u categories\u id,categories2media\u uid)
上建立索引
您可能会发现,第一个复合索引和此查询最有效:
SELECT c.*
FROM ((SELECT c.*
FROM ost_content c JOIN
ost_categories2media c2m
ON c2m.categories2media_uid = c.uid
WHERE c2m.categories2media_category_id = '53' AND
c.conversion_status = 'success' AND
c.type IN ('serial', 'media')
) UNION ALL
(SELECT c.*
FROM ost_content c JOIN
ost_categories2media c2m
ON c2m.categories2media_uid = c.uid
WHERE c2m.categories2media_category_id = '53' AND
c.conversion_status = 'announcement' AND
c.type IN ('serial', 'media')
)
) c
ORDER BY c.upload_date DESC
LIMIT 16, 16;
这看起来更复杂,但每个子查询都可以利用索引,因此可能会提高性能。首先,不需要使用左连接。因此,您可以将查询编写为:
SELECT c.*
FROM ost_content c JOIN
ost_categories2media c2m
ON c2m.categories2media_uid = c.uid
WHERE c2m.categories2media_category_id = '53' AND
c.conversion_status IN ('success', 'announcement') AND
c.type IN ('serial', 'media')
ORDER BY c.upload_date DESC
LIMIT 16, 16;
不幸的是,内容表上的条件不是简单的=
条件。如果是,建议使用ost\u内容(转换状态、类型、uid)
索引。这可能仍然是更好的选择
另一种选择是另一种方式:在ost\u categories2media(categories2media\u categories\u id,categories2media\u uid)
上建立索引
您可能会发现,第一个复合索引和此查询最有效:
SELECT c.*
FROM ((SELECT c.*
FROM ost_content c JOIN
ost_categories2media c2m
ON c2m.categories2media_uid = c.uid
WHERE c2m.categories2media_category_id = '53' AND
c.conversion_status = 'success' AND
c.type IN ('serial', 'media')
) UNION ALL
(SELECT c.*
FROM ost_content c JOIN
ost_categories2media c2m
ON c2m.categories2media_uid = c.uid
WHERE c2m.categories2media_category_id = '53' AND
c.conversion_status = 'announcement' AND
c.type IN ('serial', 'media')
)
) c
ORDER BY c.upload_date DESC
LIMIT 16, 16;
这看起来更复杂,但每个子查询都可以利用索引,因此可能会提高性能