Question

Having some real issues with a few queries, this one inparticular. Info below.

tgmp_games, about 20k rows

CREATE TABLE IF NOT EXISTS `tgmp_games` (
  `g_id` int(8) NOT NULL AUTO_INCREMENT,
  `site_id` int(6) NOT NULL,
  `g_name` varchar(255) NOT NULL,
  `g_link` varchar(255) NOT NULL,
  `g_url` varchar(255) NOT NULL,
  `g_platforms` varchar(128) NOT NULL,
  `g_added` datetime NOT NULL,
  `g_cover` varchar(255) NOT NULL,
  `g_impressions` int(8) NOT NULL,
  PRIMARY KEY (`g_id`),
  KEY `g_platforms` (`g_platforms`),
  KEY `site_id` (`site_id`),
  KEY `g_link` (`g_link`),
  KEY `g_release` (`g_release`),
  KEY `g_genre` (`g_genre`),
  KEY `g_name` (`g_name`),
  KEY `g_impressions` (`g_impressions`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1;

tgmp_reviews – about 200k rows

CREATE TABLE IF NOT EXISTS `tgmp_reviews` (
  `r_id` int(8) NOT NULL AUTO_INCREMENT,
  `site_id` int(6) NOT NULL,
  `r_source` varchar(128) NOT NULL,
  `r_date` date NOT NULL,
  `r_score` int(3) NOT NULL,
  `r_copy` text NOT NULL,
  `r_link` text NOT NULL,
  `r_int_link` text NOT NULL,
  `r_parent` int(8) NOT NULL,
  `r_platform` varchar(12) NOT NULL,
  `r_impressions` int(8) NOT NULL,
  PRIMARY KEY (`r_id`),
  KEY `site_id` (`site_id`),
  KEY `r_parent` (`r_parent`),
  KEY `r_platform` (`r_platform`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 ;

Here is the query, takes 3 seconds ish

SELECT * FROM tgmp_games g
RIGHT JOIN tgmp_reviews r ON g_id = r.r_parent
WHERE g.site_id = '34'
GROUP BY g_name
ORDER BY g_impressions DESC LIMIT 15

EXPLAIN

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
1   SIMPLE  r   ALL     r_parent    NULL    NULL    NULL    201133  Using temporary; Using filesort
1   SIMPLE  g   eq_ref  PRIMARY,site_id     PRIMARY     4   engine_comp.r.r_parent  1   Using where

I am just trying to grab the 15 most viewed games, then grab a single review (doesnt really matter which, I guess highest rated would be ideal, r_score) for each game.

Can someone help me figure out why this is so horribly inefficient?

Answer 1

1. I don’t understand what is the purpose of having a GROUP BY g_name in your query, but this makes MySQL performing aggregates on the columns selected, or all columns from both table. So please try to exclude it and check if it helps.

2. Also, RIGHT JOIN makes database to query tgmp_reviews first, which is not what you want. I suppose LEFT JOIN is a better choice here. Please, try to change the join type.

3. If none of the first options helps, you need to redesign your query. As you need to obtain 15 most viewed games for the site, the query will be:

   SELECT g_id
     FROM tgmp_games g
    WHERE site_id = 34
    ORDER BY g_impressions DESC
    LIMIT 15;
   

   This is the very first part that should be executed by the database, as it provides the best selectivity. Then you can get the desired reviews for the games:

   SELECT r_parent, max(r_score)
     FROM tgmp_reviews r
    WHERE r_parent IN (/*1st query*/)
    GROUP BY r_parent;
   

   Such construct will force database to execute the first query first (sorry for the tautology) and will give you the maximal score for each of the wanted games. I hope you will be able to use the obtained results for your purpose.