Mysql – Help creating this query

I'd like to integrate the following query:

SELECT
    parent.id
  , COUNT(child.id) AS child_count
FROM
             messages parent
  INNER JOIN messages child
    ON child.parent_id = parent.id
WHERE parent.parent_id = 0
GROUP BY parent.id;

into this query:

SELECT m.id,m.seen, m.uid, m.hash, m.date_created,m.subject,
m.textplain,m.texthtml, CONCAT_WS('@', a.localpart, a.domain ) 
AS address 
FROM messages m 
LEFT JOIN message_address_fields maf ON maf.message_id = m.id 
LEFT JOIN addresses a ON a.id = maf.address_id 
WHERE maf.field_id =4 AND m.user_id =1

Here's a sql fiddle: http://sqlfiddle.com/#!2/bef27/1

Here's my schema:

 CREATE TABLE IF NOT EXISTS `addresses` (
   `id` int(10) NOT NULL AUTO_INCREMENT,
   `user_id` int(10) NOT NULL,
   `name` text NOT NULL,
   `localpart` text NOT NULL,
   `domain` text NOT NULL,
   PRIMARY KEY (`id`)
  ) ENGINE=MyISAM  DEFAULT CHARSET=latin1;

CREATE TABLE IF NOT EXISTS `fields` (
   `id` int(10) NOT NULL AUTO_INCREMENT,
   `name` text,
  PRIMARY KEY (`id`)
 ) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=12 ;

CREATE TABLE IF NOT EXISTS `messages` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `user_id` int(10) NOT NULL,
  `account_folder_id` int(10) NOT NULL,
  `hash` varchar(255) NOT NULL,
  `subject` varchar(255) NOT NULL,
  `texthtml` text NOT NULL,
  `textplain` text NOT NULL,
  `uid` int(10) NOT NULL,
  `seen` tinyint(1) NOT NULL,
  `flagged` tinyint(1) NOT NULL,
  `date_created` int(11) NOT NULL DEFAULT '0',
  `last_modified` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`),
  UNIQUE KEY `hash` (`hash`) 
) ENGINE=MyISAM  DEFAULT CHARSET=latin1;

CREATE TABLE IF NOT EXISTS `message_address_fields` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `message_id` int(10) NOT NULL,
  `field_id` int(10) NOT NULL,
  `address_id` int(10) NOT NULL,
  `date_created` int(11) NOT NULL DEFAULT '0',
  `last_modified` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1;

Thanks for the help!

QUESTION: This query limits the data to only messages that contain an address with field id of 4. How would I make it optional to have a correlated address with a field id of 4 or not