Mysql count from a second table [duplicate]

I have a query which grabs all users from the wait table based on $oneid. This works just fine but I would like to count how many messages a user leaves. These are in another table one_msg.

function waiting_users($oneid)
    {

    $query_str ="SELECT a.user_id, b.email, b.username, b.fbook, c.user_id as saved_user, d.type as user_type,
                    FROM wait a 
                    LEFT JOIN users b ON a.user_id=b.id
                    JOIN user_profiles d ON a.user_id=d.user_id
                    LEFT JOIN save_one c ON a.user_id=c.user_id AND c.one_id=?
                    WHERE a.post_id = ? 
                    ORDER BY a.date ASC";
}
            $query = $this->db->query($query_str, array( $oneid, $oneid ) );

one_msg table

+----+--------+---------+---------+---------------------+
| id | one_id | host_id | user_id | date                |
+----+--------+---------+---------+---------------------+
|  3 |    127 |     268 |     270 | 2012-06-11 18:57:58 | 
|  4 |    127 |     268 |     270 | 2012-06-11 21:45:11 | 
|  5 |    127 |     268 |     270 | 2012-06-12 09:10:01 | 
+----+--------+---------+---------+---------------------+

So I am trying to count the messages from one_msg like this but it's returning the same value for all users.

function waiting_users($oneid)
    {

    $query_str ="SELECT a.user_id, b.email, b.username, b.fbook, c.user_id as saved_user, d.type as user_type,
                    (SELECT COUNT(id) FROM one_msg WHERE post_id = ?) AS count
                    FROM wait a 
                    LEFT JOIN users b ON a.user_id=b.id
                    JOIN user_profiles d ON a.user_id=d.user_id
                    LEFT JOIN save_one c ON a.user_id=c.user_id AND c.one_id=?
                    WHERE a.post_id = ? 
                    ORDER BY a.date ASC";

}
            $query = $this->db->query($query_str, array( $oneid, $oneid, $oneid ) );