使用MYSQL进行临时优化;使用filesort !!! - >帮助

Question

我想尝试一段时间的伙计们，我无法设法优化使用临时;从我的EXPLAIN查询中使用filesort。 行，所以，我有这个疑问：

SELECT a.adid, a.adtitle, a.addesc, scat.subcatname 
FROM ads a 
INNER JOIN cities ct ON a.cityid = ct.cityid 
INNER JOIN subcats scat ON a.subcatid = scat.subcatid 
INNER JOIN cats cat ON scat.catid = cat.catid 
WHERE a.enabled = '1' 
AND a.verified ='1' 
GROUP BY a.adid 
ORDER BY a.createdon DESC 
LIMIT 16; 

当我请务必解释一下...我得到这个：

EXPLAIN SELECT a.adid, a.adtitle, a.addesc, scat.subcatname 
FROM ads a 
INNER JOIN cities ct ON a.cityid = ct.cityid 
INNER JOIN subcats scat ON a.subcatid = scat.subcatid 
INNER JOIN cats cat ON scat.catid = cat.catid 
WHERE a.enabled = '1' 
AND a.verified ='1' 
GROUP BY a.adid 
ORDER BY a.createdon DESC LIMIT 16; 

+----+-------------+-------+--------+----------------------------------+----------+---------+--------------------------------+------+---------------------------------+ 
| id | select_type | table | type | possible_keys     | key  | key_len | ref       | rows | Extra       | 
+----+-------------+-------+--------+----------------------------------+----------+---------+--------------------------------+------+---------------------------------+ 
| 1 | SIMPLE  | cat | system | PRIMARY       | NULL  | NULL | NULL       | 1 | Using temporary; Using filesort | 
| 1 | SIMPLE  | scat | ref | PRIMARY,catid     | catid | 2  | const       | 7 |         | 
| 1 | SIMPLE  | a  | ref | subcatid,cityid,verified,enabled | subcatid | 2  | bakecai_incontri.scat.subcatid | 954 | Using where      | 
| 1 | SIMPLE  | ct | eq_ref | PRIMARY       | PRIMARY | 2  | bakecai_incontri.a.cityid  | 1 | Using index      | 
+----+-------------+-------+--------+----------------------------------+----------+---------+--------------------------------+------+---------------------------------+ 
4 rows in set (0.00 sec) 

我已经尝试了一些关键的，但没有结果：比如我创建索引createdon和adid但是mysql不会使用它。

这里是我的表中的键：

SHOW INDEX FROM ads; 

+-------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
|Table| Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | 
+-------------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| ads |   0 | PRIMARY   |   1 | adid  | A   |  8592 |  NULL | NULL |  | BTREE  |   | 
| ads |   1 | subcatid   |   1 | subcatid | A   |   9 |  NULL | NULL |  | BTREE  |   | 
| ads |   1 | cityid    |   1 | cityid  | A   |   103 |  NULL | NULL |  | BTREE  |   | 
| ads |   1 | verified   |   1 | verified | A   |   2 |  NULL | NULL | YES | BTREE  |   | 
| ads |   1 | enabled   |   1 | enabled  | A   |   2 |  NULL | NULL | YES | BTREE  |   | 
| ads |   1 | idx_createdon_adid |   1 | createdon | A   |  8592 |  NULL | NULL |  | BTREE  |   | 
| ads |   1 | idx_createdon_adid |   2 | adid  | A   |  8592 |  NULL | NULL |  | BTREE  |   | 
| ads |   1 | srch_text   |   1 | adtitle  | NULL  |   1 |  NULL | NULL | YES | FULLTEXT |   | 
| ads |   1 | srch_text   |   2 | addesc  | NULL  |   1 |  NULL | NULL | YES | FULLTEXT |   | 
| ads |   1 | srch_text   |   3 | nome  | NULL  |   1 |  NULL | NULL | YES | FULLTEXT |   | 
+-------------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
10 rows in set (0.00 sec) 

下面是表的一些简要描述：

DESCRIBE ads 
    -> ; 
+-----------+----------------------+------+-----+---------------------+----------------+ 
| Field  | Type     | Null | Key | Default    | Extra   | 
+-----------+----------------------+------+-----+---------------------+----------------+ 
| adid  | int(10) unsigned  | NO | PRI | NULL    | auto_increment | 
| nome  | varchar(255)   | YES |  | NULL    |    | 
| eta  | varchar(255)   | YES |  | NULL    |    | 
| adtitle | varchar(100)   | YES | MUL | NULL    |    | 
| addesc | text     | YES |  | NULL    |    | 
| email  | varchar(50)   | YES |  | NULL    |    | 
| phone  | varchar(255)   | YES |  | NULL    |    | 
| showemail | enum('0','1','2') | YES |  | NULL    |    | 
| code  | varchar(35)   | YES |  | NULL    |    | 
| first  | varchar(255)   | YES |  | NULL    |    | 
| cityid | smallint(5) unsigned | NO | MUL | 0     |    | 
| subcatid | smallint(5) unsigned | NO | MUL | 0     |    | 
| price  | decimal(10,2)  | NO |  | 0.00    |    | 
| hits  | int(10) unsigned  | NO |  | 0     |    | 
| ip  | varchar(15)   | YES |  | NULL    |    | 
| link  | varchar(255)   | YES |  | http://    |    | 
| verified | enum('0','1')  | YES | MUL | NULL    |    | 
| abused | int(10) unsigned  | NO |  | 0     |    | 
| enabled | enum('0','1')  | YES | MUL | NULL    |    | 
| createdon | datetime    | NO | MUL | 0000-00-00 00:00:00 |    | 
| expireson | datetime    | NO |  | 0000-00-00 00:00:00 |    | 
| timestamp | timestamp   | NO |  | CURRENT_TIMESTAMP |    | 
+-----------+----------------------+------+-----+---------------------+----------------+ 
22 rows in set (0.02 sec) 

DESCRIBE cities 
    -> ; 
+-----------+----------------------+------+-----+-------------------+----------------+ 
| Field  | Type     | Null | Key | Default   | Extra   | 
+-----------+----------------------+------+-----+-------------------+----------------+ 
| cityid | smallint(5) unsigned | NO | PRI | NULL    | auto_increment | 
| cityname | varchar(50)   | YES |  | NULL    |    | 
| regionid | smallint(5) unsigned | NO | MUL | 0     |    | 
| pos  | smallint(5) unsigned | NO | MUL | 0     |    | 
| enabled | enum('0','1')  | YES | MUL | NULL    |    | 
| timestamp | timestamp   | NO |  | CURRENT_TIMESTAMP |    | 
+-----------+----------------------+------+-----+-------------------+----------------+ 
6 rows in set (0.00 sec) 

DESCRIBE cats 
    -> ; 
+-----------+----------------------+------+-----+-------------------+----------------+ 
| Field  | Type     | Null | Key | Default   | Extra   | 
+-----------+----------------------+------+-----+-------------------+----------------+ 
| catid  | smallint(5) unsigned | NO | PRI | NULL    | auto_increment | 
| catname | varchar(50)   | YES |  | NULL    |    | 
| pos  | smallint(5) unsigned | NO |  | 0     |    | 
| enabled | enum('0','1')  | YES | MUL | NULL    |    | 
| timestamp | timestamp   | NO |  | CURRENT_TIMESTAMP |    | 
+-----------+----------------------+------+-----+-------------------+----------------+ 
5 rows in set (0.00 sec) 

任何帮助，我很感激！

Answer 1

SELECT a.adid, a.adtitle, a.addesc, scat.subcatname 
FROM ads a 
INNER JOIN 
     subcats scat 
ON  a.subcatid = scat.subcatid 
WHERE a.enabled = '1' 
     AND a.verified ='1' 
ORDER BY a.createdon 
     DESC 
LIMIT 16 

删除不需要的连接，并摆脱不需要的GROUP BY。

为了摆脱filesort，创建下列指标：

CREATE INDEX ix_ads_e_v_created ON ads (enabled, verified, createdon) 

Answer 2

你需要玩弄迫使指数 - here you will find more information。然而在你的情况下，它并没有什么帮助，因为你使用不同的索引来进行连接和组合，所以mysql没有机会“重用”它们。

Answer 3

OK，它改善，但现在查询扫描所有的行： --hmm我想这是因为所有的线已经启用并验证等于1 ......从什么

EXPLAIN SELECT a.adid, a.adtitle, a.addesc, scat.subcatname 
    -> FROM ads a 
    -> INNER JOIN subcats scat 
    -> ON a.subcatid = scat.subcatid 
    -> WHERE a.enabled = '1' 
    -> AND a.verified ='1' 
    -> ORDER BY a.createdon DESC 
    -> LIMIT 16; 
+----+-------------+-------+--------+----------------------------------------------+--------------------+---------+-----------------------------+------+-------------+ 
| id | select_type | table | type | possible_keys        | key    | key_len | ref       | rows | Extra  | 
+----+-------------+-------+--------+----------------------------------------------+--------------------+---------+-----------------------------+------+-------------+ 
| 1 | SIMPLE  | a  | ref | subcatid,verified,enabled,ix_ads_e_v_created | ix_ads_e_v_created | 4  | const,const     | 8485 | Using where | 
| 1 | SIMPLE  | scat | eq_ref | PRIMARY          | PRIMARY   | 2  | bakecai_incontri.a.subcatid | 1 |    | 
+----+-------------+-------+--------+----------------------------------------------+--------------------+---------+-----------------------------+------+-------------+ 
2 rows in set (0.00 sec) 

我知道我必须编制索引吗？但在哪些列/列？

Answer 4

只是为了笑容......改变

SELECT STRAIGHT_JOIN（查询的其余部分）

通过让子类表是小，优化引擎将尝试使用它作为查询和NOT的基础查询中的第一个表...这一个关键词“STRAIGHT_JOIN”帮助我在过去30多个小时内将超过14百万条记录加入到15个查找表中，以将这个过程挂起，持续时间不超过2小时去完成。