在一个MySQL查询中使用两个LEFT OUTER JOINS时，如果first为空则不会触发

Question

I am trying to build a feed for a photography site I am building. Below is the query to get all activity that has happened in the previous DAY. This works perfectly if there is a comment left in the last day(the first LEFT OUTER JOIN) but if only likes have happened(the second LEFT OUTER JOIN) then this returns empty. I think the problem is if the first LEFT OUTER JOIN is empty then the second one seems to not fire. If I am right in this assumption do you have any idea how to get the second to fire regardless of the outcome of the first.

SELECT a.a_id
            , a.a_user_id
            , a.a_activity_type
            , a.a_activity_id
            , a.a_activity_time
            , c.ic_id 
            , c.ic_status
            , c.ic_image_id
            , c.ic_creator_id
            , c.ic_comment
            , c.ic_read_status
            , s.id 
            , s.image_id 
            , s.photographer_id
            , s.user_id
            , u.u_id
            , u.u_screen_name
            , u.u_url_screen_name
            , u.u_email
            , u.u_avatar
            , u1.u_id as currentUser
            , u1.u_email as currentEmail
            , u1.u_url_screen_name as currentScreenName
            , i.i_id
            , i.i_name
            , COALESCE(c.ic_image_id, s.image_id) as image_id
            , COALESCE(c.ic_creator_id, s.photographer_id) as other_user_id
            FROM activity AS a
                LEFT OUTER JOIN image_comments as c ON 
                a.a_activity_id = c.ic_id AND a.a_activity_type = 1
                LEFT OUTER JOIN site_likes as s ON 
                a.a_activity_id = s.id AND a.a_activity_type = 2
                LEFT JOIN users as u ON
                u.u_id = COALESCE(c.ic_creator_id, s.photographer_id)
                LEFT JOIN images as i ON
                i.i_id = COALESCE(c.ic_image_id, s.image_id)
                LEFT JOIN users as u1 ON
                u1.u_id = a.a_user_id
            WHERE a.a_activity_time >= DATE_SUB(now(), INTERVAL 1 DAY)
            AND
            COALESCE(c.ic_creator_id, s.photographer_id) != a.a_user_id
            ORDER BY a.a_activity_time DESC

UPDATE: Upon further testing it seems the COALESCE() in the WHERE clause is the problem. One of these fields will always have a value while the other will not. If I get rid of this the query works fine which is good because I can use it as is and then in the application remove what I need to remove but I would still really like this to work in the query.