どうですか:
select teams.`team_name`, count(matches.`played_team`)
from teams
join matches on teams.`team_number` = matches.`played_team`
group by teams.`team_name`
使用したテーブルは次のとおりです。
CREATE TABLE `teams` (
`team_number` int(11) NOT NULL AUTO_INCREMENT,
`team_name` varchar(30) DEFAULT NULL,
PRIMARY KEY (`team_number`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
INSERT INTO `teams` (`team_number`, `team_name`)
VALUES
(1,'a'),
(2,'b'),
(3,'c'),
(4,'d');
CREATE TABLE `matches` (
`played_team` int(11) NOT NULL,
`id` int(11) NOT NULL AUTO_INCREMENT,
`match_title` varchar(30) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `played_team` (`played_team`),
CONSTRAINT `matches_ibfk_1` FOREIGN KEY (`played_team`) REFERENCES `teams` (`team_number`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
INSERT INTO `matches` (`played_team`, `id`, `match_title`)
VALUES
(1,1,'match_a'),
(1,2,'match_b'),
(3,3,'match_c'),
(4,4,'match_d');
クエリの結果は次のとおりです。
team_name count(matches.`played_team`)
a 2
c 1
d 1