Question

hopefully somebody can help me with this query. I need to list all 200 records from ngr_titles below, joined with their most recent related record from ngr_monitordata. The foreign key in ngr_monitordata is called titleid and the most recent should be the higher when_posted value for each title.
The problem is that ngr_monitordata contains millions of records and is increasing every second.

This is the query I used but it takes 14 seconds to execute:

SELECT * FROM ngr_titles
LEFT JOIN 
(SELECT titleid, MAX(when_posted) FROM ngr_monitordata GROUP BY titleid) tmp1
ON ngr_titles.id= tmp1.titleid;

What would be the best approach?

Tables are:

CREATE TABLE `ngr_titles` (
  `id` int(11) NOT NULL auto_increment,
  `title` varchar(255) default NULL,
  `drop_min` int(11) NOT NULL default '50',
  `warn_pcnt` float(5,1) NOT NULL default '15.0',
  `crit_pcnt` float(5,1) NOT NULL default '25.0',
  `deviations` float(5,1) NOT NULL default '2.0',
  `addlobby` int(2) NOT NULL default '0',
  `url` varchar(255) default NULL,
  `graph_url` varchar(255) default NULL,
  `lastchecked` int(11) NOT NULL default '0',
  `last_exception` int(11) default NULL,
  `state` enum('ok','warning','critical') default NULL,
  `trend` int(11) NOT NULL default '0',
  `short_name` varchar(45) NOT NULL,
  `historical` varchar(45) NOT NULL,
  `cacti_url` varchar(255) default NULL,
  PRIMARY KEY  (`id`),
  UNIQUE KEY `title` (`title`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;



CREATE TABLE `ngr_monitordata` (
  `id` int(11) NOT NULL auto_increment,
  `titleid` int(11) default NULL,
  `when_posted` int(11) default NULL,
  `games_completed` int(11) default NULL,
  `games_created` int(11) default NULL,
  `games_in_progress` int(11) default NULL,
  `games_in_progress_gps` int(11) default NULL,
  `users_in_games` int(11) default NULL,
  `users_in_games_gps` int(11) default NULL,
  `users_in_lobby` int(11) default NULL,
  `users_in_passive` int(11) default NULL,
  `users_in_rooms` int(11) default NULL,
  `rooms` int(11) default NULL,
  `state` enum('ok','warning','critical','unknown') NOT NULL default 'ok',
  `user_drop` int(11) NOT NULL default '0',
  `retries` int(8) default NULL,
  PRIMARY KEY  (`id`),
  UNIQUE KEY `whowhenidx` (`titleid`,`when_posted`),
  KEY `whenidx` (`when_posted`),
  KEY `titleidx` (`titleid`),
  KEY `stateidx` (`state`)
) ENGINE=MyISAM AUTO_INCREMENT=120512615 DEFAULT CHARSET=utf8;

Answer 1

SELECT 
    t.*
FROM 
    ngr_titles t 
INNER JOIN 
ngr_monitordata m
    ON 
t.id = m.titleid 
    AND 
m.when_posted = (SELECT MAX(when_posted) FROM ngr_monitordata WHERE titleid = t.id)

Quick solution, it should work although I wrote it in haste. If it were me, I’d normalize the data slightly to reduce the overhead from aggregate function and subquery.