如何通过已使用索引的查询加快组的速度？

Question

我们有一个MyISAM表,大约有75百万行,有5列:

id (int), 
user_id(int), 
page_id (int), 
type (enum with 6 strings)
date_created(datetime).

我们在ID列上有一个主索引,一个唯一索引(user_id,page_id,date_created)和一个复合索引(page_id,date_created)

问题是以下查询最多需要90秒才能完成

SELECT SQL_NO_CACHE user_id, count(id) nr 
FROM `table` 
WHERE `page_id`=301 
and `date_created` BETWEEN '2012-01-03' AND '2012-02-03 23:59:59' 
AND page_id<>user_id 
group by `user_id`

这是此查询的解释

+----+-------------+----------------------------+-------+---------------+---------+---------+------+--------+----------------------------------------------+
| id | select_type | table                      | type  | possible_keys | key     | key_len | ref  | rows   | Extra                                        |
+----+-------------+----------------------------+-------+---------------+---------+---------+------+--------+----------------------------------------------+
|  1 | SIMPLE      | table                      | range | page_id       | page_id | 12      | NULL | 520024 | Using where; Using temporary; Using filesort |
+----+-------------+----------------------------+-------+---------------+---------+---------+------+--------+----------------------------------------------+

编辑: 在ypercube的建议下,我尝试添加一个新索引(page_id,user_id,date_created).但是mysql不使用它默认,所以我不得不建议查询优化器.这是新查询和解释:

SELECT SQL_NO_CACHE user_id, count(*) nr FROM `table` USE INDEX (usridexp) WHERE `page_id`=301 and `date_created` BETWEEN '2012-01-03' AND '2012-02-03 23:59:59' AND page_id<>user_id group by `user_id` ORDER BY NULL


    +----+-------------+----------------------------+------+---------------+----------+---------+-------+---------+--------------------------+
    | id | select_type | table                      | type | possible_keys | key      | key_len | ref   | rows    | Extra                    |
    +----+-------------+----------------------------+------+---------------+----------+---------+-------+---------+--------------------------+
    |  1 | SIMPLE      | table                      | ref  | usridexp      | usridexp | 4       | const | 3943444 | Using where; Using index |
    +----+-------------+----------------------------+------+---------------+----------+---------+-------+---------+--------------------------+

Answer 1

一些可能改进查询的更改:

• 更改COUNT(id)到COUNT(*).因为id(我猜)PRIMARY KEY NOT NULL,结果将是相同的.

• 添加一个ORDER BY NULL后续GROUP BY条款.在MySQL中,按操作分组也会对结果进行排序,除非您指定其他方式.

• 这(page_id, date_created)可能是MySQL可以用于此查询的最佳索引,但您也可以尝试(page_id, user_id, date_created)(如果添加此索引,还可以发布EXPLAIN吗？)

另一个与此查询的性能无关的事情:

如果您(user_id, page_id, date_created)是UNIQUE和id自动生成(并且不用于除主键之外的任何其他内容),您可以将其作为PRIMARY KEY并删除id列.少一个索引,每行少4个字节.