Question

How can a sort by user popularity when using a hasAndBelongsToMany table relationship? ie:

I have a table called playgroups, players, and playgroup_players.

How can I sort playgroups by the number of players in the playgroup?

Playgroups:

CREATE TABLE `playgroups` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  `tag` varchar(4) COLLATE utf8_unicode_ci DEFAULT NULL,
  `description` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `avatar_url` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `city` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `state` varchar(2) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=8 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

Players:

CREATE TABLE `players` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `first_name` varchar(30) DEFAULT NULL,
  `last_name` varchar(30) DEFAULT NULL,
  `username` varchar(30) NOT NULL,
  `password` varchar(255) NOT NULL,
  `email` varchar(255) NOT NULL,
  `public_email` tinyint(1) NOT NULL DEFAULT '0',
  `facebook_id` varchar(250) DEFAULT NULL,
  `card_tooltip` tinyint(1) NOT NULL DEFAULT '1',
  `profile_pic_url` varchar(255) NOT NULL,
  `public_name` tinyint(1) NOT NULL DEFAULT '0',
  `city` varchar(40) NOT NULL,
  `state` varchar(2) NOT NULL,
  `date_joined` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=107 DEFAULT CHARSET=latin1;

And PlaygroupPlayers:

CREATE TABLE `playgroup_players` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `player_id` int(11) NOT NULL,
  `playgroup_id` int(11) NOT NULL,
  `admin` tinyint(1) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

Answer 1

SELECT PP.playgroup_id, COUNT(*) cnt
FROM playgroup_players PP
GROUP BY PP.playgroup_id
ORDER BY COUNT(*) DESC

This will give you a list of playgroups that have at least one player sorted by the number of players. Of course, field name is made up 🙂

SELECT G.playgroup_id, COUNT(PP.playgroup_id) cnt
FROM playgroup G
  LEFT OUTER JOIN playgroup_players PP ON (PP.playgroup_id=G.playgroup_id)
GROUP BY G.playgroup_id
ORDER BY COUNT(*) DESC

This should give you a list of ALL playgroups (even the ones with no players). I’ve tested this on Oracle and on some of my own data and it works