Mysql query with inner subquery and where,order,group not use indexes

Question

all. I have 2 mysql tables type myisam

CREATE TABLE `users` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL DEFAULT '',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

CREATE TABLE `users_ratings` (
  `id` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
  `created_date` varchar(255) DEFAULT NULL,
  `user_id` mediumint(9) DEFAULT NULL,
  `rating1` mediumint(9) DEFAULT NULL,
  `rating2` mediumint(9) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

Dump can be downloaded here

I want all users to select and sort the list by rating2 and rating2 must be > 1000

SELECT * FROM users as u 
INNER JOIN (SELECT rating2, user_id,MAX(created_date) as maxdate FROM `users_ratings` GROUP BY user_id) as x ON x.user_id = u.id 
INNER JOIN users_ratings as ur ON(ur.created_date = x.maxdate and ur.user_id = u.id) 
WHERE x.rating2 > 1000 
ORDER by ur.rating2

Without such an index the query is executed for 9 seconds.

All possible codes, which I thought was allowed to reduce the time of the request to 1-2 seconds.

Help the right to place indexes

Answer 1

I suspect you want the following query. Assuming you do, and performance is still an issue, provide the EXPLAIN for same...

(this assumes a Unique Key on user_id,[rating2,]created_date, which hasn't actually been specified)

SELECT u.*
     , x.*
  FROM users u 
  JOIN users_ratings x
    ON x.user_id = u.id
  JOIN 
     ( SELECT user_id
            , MAX(created_date) maxdate 
         FROM users_ratings
        WHERE rating2 > 1000
        GROUP 
           BY user_id
     ) y 
    ON y.user_id = x.user_id 
   AND y.maxdate = x.created_date
 ORDER 
    BY x.rating2;