非常慢的查询： <derived2> 使用临时的；使用文件排序
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【中文标题】非常慢的查询： <derived2> 使用临时的；使用文件排序【英文标题】：Very slow query with: <derived2> Using temporary; Using filesort 【发布时间】：2013-09-08 21:54:17 【问题描述】：我的选择类别查询 Restructuring a DB for best performance 出现性能问题 所以我设定了一个目标来解决它。但最终结果证明这是一个更复杂的查询，与原始查询相比，性能实际上有所下降。
SELECT *
FROM post
LEFT JOIN post_plus
ON ( post.id = post_plus.news_id )
INNER JOIN (SELECT DISTINCT c1.postid
FROM post_category c1
JOIN post_category c2
ON c1.postid = c2.postid
WHERE c1.categoryid IN ( 130, 3, 4, 5 )
AND c2.categoryid = 73) post_category
ON ( post_category.postid = post.id )
WHERE approve = 1
ORDER BY fixed DESC,
date DESC
LIMIT 0, 7;
新查询需要：（1.02 秒）- 使用正则表达式的旧查询耗时（0.23 秒）
我只能猜测是因为Using temporary; Using filesort
我怎样才能摆脱这个？
解释查询：
`+----+-------------+---------------+--------+-------------------+------------+---------+--------------------------+-------+----------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------------+--------+-------------------+------------+---------+--------------------------+-------+----------------------------------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 10470 | Using temporary; Using filesort |
| 1 | PRIMARY | post | eq_ref | PRIMARY,approve | PRIMARY | 4 | post_category.postid | 1 | Using where |
| 1 | PRIMARY | post_plus | ref | news_id | news_id | 5 | post_category.postid | 1 | NULL |
| 2 | DERIVED | c1 | range | postId,categoryId | categoryId | 2 | NULL | 10470 | Using index condition; Using temporary |
| 2 | DERIVED | c2 | ref | postId | postId | 4 | online_test.c1.postId | 1 | Using index |
+----+-------------+---------------+--------+-------------------+------------+---------+--------------------------+-------+----------------------------------------+
`
张贴表
| post | CREATE TABLE `post` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`autor` varchar(40) NOT NULL DEFAULT '',
`date` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`short_story` text NOT NULL,
`full_story` text NOT NULL,
`xfields` text NOT NULL,
`title` varchar(255) NOT NULL DEFAULT '',
`descr` varchar(200) NOT NULL DEFAULT '',
`keywords` text NOT NULL,
`category` varchar(200) NOT NULL DEFAULT '0',
`alt_name` varchar(200) NOT NULL DEFAULT '',
`comm_num` mediumint(8) unsigned NOT NULL DEFAULT '0',
`allow_comm` tinyint(1) NOT NULL DEFAULT '1',
`allow_main` tinyint(1) unsigned NOT NULL DEFAULT '1',
`approve` tinyint(1) NOT NULL DEFAULT '0',
`fixed` tinyint(1) NOT NULL DEFAULT '0',
`allow_br` tinyint(1) NOT NULL DEFAULT '1',
`symbol` varchar(3) NOT NULL DEFAULT '',
`tags` varchar(255) NOT NULL DEFAULT '',
`metatitle` varchar(255) NOT NULL DEFAULT '',
`FileTempUUID` varchar(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `autor` (`autor`),
KEY `alt_name` (`alt_name`),
KEY `category` (`category`),
KEY `allow_main` (`allow_main`),
KEY `date` (`date`),
KEY `symbol` (`symbol`),
KEY `comm_num` (`comm_num`),
KEY `tags` (`tags`),
KEY `descr` (`descr`),
KEY `title` (`title`),
KEY `approve` (`approve`,`allow_main`),
FULLTEXT KEY `full_story` (`full_story`),
FULLTEXT KEY `short_story` (`short_story`,`full_story`,`xfields`,`title`),
FULLTEXT KEY `title_2` (`title`)
) ENGINE=InnoDB AUTO_INCREMENT=32586 DEFAULT CHARSET=utf8 |
post_plus
| post_plus | CREATE TABLE `post_plus` (
`pid` int(11) NOT NULL AUTO_INCREMENT,
`news_id` int(11) DEFAULT NULL,
`kp_id` varchar(100) CHARACTER SET utf8 DEFAULT NULL,
`pdate` datetime DEFAULT NULL,
`news_read` int(11) NOT NULL DEFAULT '0',
`user_id` int(11) NOT NULL DEFAULT '0',
`allow_rate` tinyint(1) NOT NULL DEFAULT '1',
`rating` mediumint(8) NOT NULL DEFAULT '0',
`vote_num` mediumint(8) NOT NULL DEFAULT '0',
`votes` tinyint(1) NOT NULL DEFAULT '0',
`editdate` int(11) DEFAULT NULL,
`view_edit` tinyint(1) NOT NULL DEFAULT '0',
`editor` varchar(40) CHARACTER SET utf8 NOT NULL DEFAULT '',
`reason` varchar(255) CHARACTER SET utf8 NOT NULL DEFAULT '',
`access` varchar(150) CHARACTER SET utf8 NOT NULL DEFAULT '',
PRIMARY KEY (`pid`),
KEY `user_id` (`user_id`),
KEY `news_id` (`news_id`)
) ENGINE=InnoDB AUTO_INCREMENT=32819 DEFAULT CHARSET=latin1 |
post_category 表
| post_category | CREATE TABLE `post_category` (
`cid` bigint(11) NOT NULL AUTO_INCREMENT,
`postId` int(11) NOT NULL,
`categoryId` smallint(6) NOT NULL,
PRIMARY KEY (`cid`),
KEY `postId` (`postId`,`categoryId`),
KEY `categoryId` (`categoryId`)
) ENGINE=InnoDB AUTO_INCREMENT=100870 DEFAULT CHARSET=latin1 |
【问题讨论】：
真的 - 除了 EXPLAIN 计划 - 你应该显示所有表的定义（SHOW CREATE TABLE tablename; 的输出），以便我们知道数据类型、主键和外键、索引。
你能添加一个(categoryId, postId)索引并更新效率和新的解释吗？
为什么第二个LEFT JOIN（到派生表）首先是LEFT连接？看起来应该是 INNER 加入。
是的，它是内在的。复制了旧代码...我在 post_category 表中有 KEY postId (postId,categoryId), KEY categoryId (categoryId) ` 的键
在(categoryId, postId) 上再添加一个、复合、索引，您可以删除(categoryId) 一个。
【参考方案1】：
我认为这个查询在精神上是等效的，并且可能执行得更快。特别是如果您在 post_category (postid, categoryid) 上创建索引
Select
*
From
post
Left Join
post_plus
On post.id = post_plus.news_id
Where
Exists (
Select
'x'
From
post_category c1
Where
categoryid = 73 and
c1.postid = post.postid
) And
Exists (
Select
'x'
From
post_category c2
Where
categoryid In (130, 3, 4, 5) and
c2.postid = post.postid
) And
approve = 1
Order By
fixed Desc,
date Desc
Limit
0, 7;
由于postid, categoryid 在post_category 上是唯一的，您也可以这样重写它。它可能会受益于相反顺序的索引(categoryid, postid)：
Select
post.*,
post_plus.*
From
post_category c1
Inner Join
post
On c1.categoryid = 73 and c1.postid = post.postid
Left Join
post_plus
On post.id = post_plus.news_id
Where
Exists (
Select
'x'
From
post_category c2
Where
categoryid In (130, 3, 4, 5) and
c2.postid = post.postid
) And
approve = 1
Order By
fixed Desc,
date Desc
Limit
0, 7;
【讨论】：
【参考方案2】：由于每个帖子（最多）只有一个 post_plus，因此您可以先限制，然后将连接应用到 post_plus，使用您的查询或 Laurence 的重写（或任何其他等效项）。以下是 Laurence 的查询以这种方式重写并稍作修改：
Select
p.*, pp.*
From
( Select
post.id
From
post
Where
Exists (
Select
'x'
From
post_category As c1
Where
c1.categoryid = 73 And
c1.postid = post.postid
) And
Exists (
Select
'x'
From
post_category As c2
Where
c2.categoryid In (130, 3, 4, 5) And
c2.postid = post.postid
) And
post.approve = 1
Order By
post.fixed Desc,
post.date Desc
Limit
0, 7
) As lim
Join
post AS p
On lim.id = p.id
Left Join
post_plus As pp
On lim.id = pp.news_id
Order By
p.fixed Desc,
p.date Desc ;
【讨论】：
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