[英]mysql select from table 1 join and order by table 2 , optimization filesort
阅读mysql的帖子,但找不到解决方案。
任何指针将不胜感激。
我有2个表A,B表A的folderid映射到多个feedid(1到许多),而表B的feedid和与其关联的数据。
以下查询给出了使用索引; 使用临时; 使用文件排序
SELECT A.feed_id,B.feed_id,B.entry_id
FROM feed_folder A
LEFT JOIN feed_data B on A.feed_id=B.feed_id
WHERE A.folder_id=29
AND B.entry_id <= 123
AND B.entry_created <= '2012-11-01 21:38:54'
ORDER by B.entry_created desc limit 0,20;
关于如何避免临时文件排序的任何想法。
以下是表结构
CREATE TABLE `feed_folder` (
`folder_id` bigint(20) unsigned NOT NULL,
`feed_id` bigint(20) unsigned NOT NULL,
UNIQUE KEY `folder_id` (`folder_id`,`feed_id`),
KEY `feed_id` (`feed_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
CREATE TABLE `feed_data` (
`entry_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`feed_id` bigint(20) unsigned NOT NULL,
`entry_created` datetime NOT NULL,
`entry_object` text,
`entry_permalink` varchar(150) NOT NULL,
`entry_orig_created` datetime NOT NULL,
PRIMARY KEY (`entry_id`),
UNIQUE KEY `feed_id_2` (`feed_id`,`entry_permalink`),
KEY `entry_created` (`entry_created`),
KEY `feed_id` (`feed_id`,`entry_created`),
KEY `feed_id_entry_id` (`feed_id`,`entry_id`),
KEY `entry_permalink` (`entry_permalink`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8
试试这个查询:
SELECT * FROM(SELECT
A.feed_id,B.feed_id,B.entry_id
FROM feed_folder as A
INNER JOIN feed_data as B on A.feed_id=B.feed_id
WHERE A.folder_id=29
AND B.entry_id <= 123
AND B.entry_created <= '2012-11-01 21:38:54')joinAndSortTable
ORDER by B.entry_created desc limit 0,20;
问题是别名,您忘了给as A
和as B
提示,我也提醒您有关LEFT JOIN和RIGHT JOIN,INNER JOIN ...要联接您选择的所有记录,使用INNER JOIN
是一种解决方法。 因为INNER JOIN
可以连接具有完全访问INNER JOIN
所有列。
祝好运
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