MYSQL优化用于临时; 使用filesort !!! - >帮助

Question

Guys I'm trying for some time now and I can't manage to optimize the Using temporary; Using filesort from my EXPLAIN query. OK so, I have this query:

 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;

When I do EXPLAIN ... I get this:

    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)

I have tried some KEY's but no result: for example I create an index for createdon and adid but mysql won't use it.

Here are the keys for my table:

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)

HERE are some brief description of the tables:

 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)

Any help , i appreciate!

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

Removed unneeded joins and got rid of unneeded GROUP BY .

To get rid of filesort , create the following index:

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

Answer 2

You need to play around with forcing indices - here you will find more information . However in you case it won't help much, because you use different indices for joins and for groups so mysql has no chance to "reuse" them.

Answer 3

OK, it improved but now the query is scanning all the rows: --hmm i think this is because all of the lines have enabled and verified equal to 1...

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)

From what I know I have to make an index right? but on wich column/columns?

Answer 4

Just for grins... change to

SELECT STRAIGHT_JOIN (rest of your query)

By having the subcategory table being small, the optimizer engine will try to use that as basis of querying and NOT the first table in the query... This one keyword "STRAIGHT_JOIN" has helped me in the past doing gov't queries of 14+ million records joined to 15+ lookup tables from hanging the process after 30+ hours to less than 2 hours to complete.