MySQL查询慢，按订单按限额分组

Question

我目前加入了5个表来选择20个对象显示给用户，不幸的是，如果我使用group by和order by，它会变得非常慢。

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 

查询的解释显示如下：

+------+-------------+-------+--------+----------------------------+------------+---------+---------------------------------------+--------+--------------------------------------------------------+
| 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 |                                                        |
+------+-------------+-------+--------+----------------------------+------------+---------+---------------------------------------+--------+--------------------------------------------------------+

所以看起来它没有为objekte表使用键，分析说明它使用2.7s复制到tmp表。

没有使用from Angebote或join objekte，我尝试使用(SELECT*GROUP BY id)，但不幸的是，这没有改善。

我想我错过了一些基本的概念在这里和任何帮助将是感激的。

由于很可能是我弄错了表，下面是对表的描述：

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 | 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（结构相同）

+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 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 |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Answer 1

首先，这是一个不规范的群体。因此，当您升级到MySQL5.7时，它将停止工作。

最大的问题来自于在objekte表上没有使用索引。更糟糕的是，您正在对该表的评级字段进行排序，但索引仍未使用。一个可能的解决方案是创建一个复合索引，如下所示：

CREATE INDEX objekte_idx ON objekte(id,rating);