[英]Slow MySQL Query, Group By Order By Limit
我目前加入5个表来选择20个对象来显示用户,不幸的是,如果我使用GROUP BY
和ORDER BY
它变得非常慢。
示例查询看起来像这样:
SELECT r.name, l.name, o.typ, o.id, persons, children, description, rating, totalratings, minprice, picture FROM angebote as a
JOIN objekte as o ON a.fid_objekt = o.id
JOIN regionen as r ON a.fid_region = r.id
JOIN laender as l ON a.fid_land = l.id
WHERE l.slug="aegypten" AND a.letztes_angebot >= 1
GROUP BY a.fid_objekt ORDER BY rating DESC LIMIT 0,20
查询的EXPLAIN显示:
+------+-------------+-------+--------+----------------------------+------------+---------+---------------------------------------+--------+--------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+-------+--------+----------------------------+------------+---------+---------------------------------------+--------+--------------------------------------------------------+
| 1 | SIMPLE | l | ref | PRIMARY,slug | slug | 767 | const | 1 | Using index condition; Using temporary; Using filesort |
| 1 | SIMPLE | o | ALL | PRIMARY | NULL | NULL | NULL | 186779 | Using join buffer (flat, BNL join) |
| 1 | SIMPLE | a | ref | unique_key,letztes_angebot | unique_key | 8 | ferienhaeuser.o.id,ferienhaeuser.l.id | 1 | Using where |
| 1 | SIMPLE | r | eq_ref | PRIMARY | PRIMARY | 4 | ferienhaeuser.a.fid_region | 1 | |
+------+-------------+-------+--------+----------------------------+------------+---------+---------------------------------------+--------+--------------------------------------------------------+
因此看起来它没有使用表objekte
的密钥,Profiling说它使用2.7s来复制到tmp表。
而不是FROM angebote
或JOIN objekte
我尝试了它(SELECT * GROUP BY id)
但遗憾的是这没有改进。
用于WHERE
, ORDER BY
和GROUP BY
的字段也被编入索引。
我想我在这里错过了一些基本概念,任何帮助将不胜感激。
因为我最有可能在表格中犯了错误,这里描述了它们:
Objekte
+---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | objekte | CREATE TABLE `objekte` ( `id` int(11) NOT NULL, `typ` varchar(50) NOT NULL, `persons` int(11) NOT NULL, `children` int(11) NOT NULL, `description` text NOT NULL, `rating` float NOT NULL, `totalratings` int(11) NOT NULL, `minprice` float NOT NULL, `picture` varchar(255) NOT NULL, `last_offer` int(11) NOT NULL, PRIMARY KEY (`id`), KEY `minprice` (`minprice`), KEY `rating` (`rating`), KEY `last_offer` (`last_offer`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | +---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
Angebote
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | angebote | CREATE TABLE `angebote` ( `id` int(11) NOT NULL AUTO_INCREMENT, `fid_objekt` int(11) NOT NULL, `fid_land` int(11) NOT NULL, `fid_region` int(11) NOT NULL, `fid_subregion` int(11) NOT NULL, `letztes_angebot` int(11) NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `unique_key` (`fid_objekt`,`fid_land`,`fid_region`,`fid_subregion`), KEY `letztes_angebot` (`letztes_angebot`), KEY `fid_objekt` (`fid_objekt`), KEY `fid_land` (`fid_land`), KEY `fid_region` (`fid_region`), KEY `fid_subregion` (`fid_subregion`) ) ENGINE=InnoDB AUTO_INCREMENT=2433073 DEFAULT CHARSET=utf8 | +-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
laender,regionen,subregionen(相同结构)
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | laender | CREATE TABLE `laender` ( `id` int(11) NOT NULL AUTO_INCREMENT, `iso` varchar(2) NOT NULL, `name` varchar(255) NOT NULL, `slug` varchar(255) NOT NULL, `letztes_angebot` int(11) NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `iso` (`iso`), KEY `slug` (`slug`), KEY `letztes_angebot` (`letztes_angebot`) ) ENGINE=InnoDB AUTO_INCREMENT=107 DEFAULT CHARSET=utf8 | +---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
首先,这是一个非标准组。 因此,当您升级到mysql 5.7时它将停止工作。
最大的问题来自objekte
表上没有使用索引的事实。 更糟糕的是,您要在该表的评级字段中进行排序,但索引仍未使用。 一种可能的解决方案是创建一个这样的复合索引:
CREATE INDEX objekte_idx ON objekte(id,rating);
您不需要在这里使用GROUP BY。 您还没有使用聚合函数。 因此从查询中删除GROUP BY。 删除Group By将提高查询性能。 也无需为限制定义0。
SELECT r.name, l.name, o.typ, o.id, persons, children, description, rating, totalratings, minprice, picture FROM angebote as a
JOIN objekte as o ON a.fid_objekt = o.id
JOIN regionen as r ON a.fid_region = r.id
JOIN laender as l ON a.fid_land = l.id
WHERE l.slug="aegypten" AND a.letztes_angebot >= 1
ORDER BY rating DESC LIMIT 20
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