MySQL查詢速度慢，按訂單限制分組

Question

我目前加入5個表來選擇20個對象來顯示用戶，不幸的是，如果我使用GROUP BY和ORDER BY它變得非常慢。

示例查詢看起來像這樣：

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 

查詢的EXPLAIN顯示：

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

因此看起來它沒有使用表objekte的密鑰，Profiling說它使用2.7s來復制到tmp表。

而不是FROM angebote或JOIN objekte我嘗試了它(SELECT * GROUP BY id)但遺憾的是這沒有改進。

用於WHERE ， ORDER BY和GROUP BY的字段也被編入索引。

我想我在這里錯過了一些基本概念，任何幫助將不勝感激。

因為我最有可能在表格中犯了錯誤，這里描述了它們：

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（相同結構）

+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 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，這是一個非標准組。 因此，當您升級到mysql 5.7時它將停止工作。

最大的問題來自objekte表上沒有使用索引的事實。 更糟糕的是，您要在該表的評級字段中進行排序，但索引仍未使用。 一種可能的解決方案是創建一個這樣的復合索引：

CREATE INDEX objekte_idx ON objekte(id,rating);

Answer 2

您不需要在這里使用GROUP BY。 您還沒有使用聚合函數。 因此從查詢中刪除GROUP BY。 刪除Group By將提高查詢性能。 也無需為限制定義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