问如何显示MySQL数据库中每月的记录数(包括零)？

EN

CREATE TABLE IF NOT EXISTS `members` (
  `id` int(11) NOT NULL,
  `group_id` int(11) NOT NULL,
  `name` varchar(64) NOT NULL,
  `joined` datetime NOT NULL,
  KEY `id` (`id`),
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

CREATE TABLE IF NOT EXISTS `blocker` (
    `group_id` int(11) NOT NULL,
    `YYYYMM` char(7) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

  SELECT date_format( m.joined, '%Y-%m' ) AS DateJoined, count( * ) AS NumJoined 
  FROM members AS m
  LEFT OUTER JOIN blocker AS b
  ON b.YYYYMM = date_format( m.joined, '%Y-%m')
  WHERE m.group_id =1637017 AND b.group_id =1637017
  GROUP BY DateJoined
  ORDER BY DateJoined ASC

DateJoined  NumJoined 
2012-01     0
2012-02     0
2012-03     0
2012-04     17
2012-05     0
2012-06     12
2012-07     10
2012-08     10
2012-09     11
2012-10     14
2012-11     4

DateJoined  NumJoined 
2012-04     17
2012-06     12
2012-07     10
2012-08     10
2012-09     11
2012-10     14
2012-11     4