SELECT 

mfd.forum AS 'forum_id',

IF(mfm.`scale`=0, "Not Rating","Rating") AS 'forum_type',

mcc.fullname AS 'coursename',

mfm.name AS 'activity',

mfd.name AS 'discussion',

CONCAT(mfp.subject,' | ',mfp.message) AS 'reply',

mfp.userid,

mus.firstname AS 'name',

mus.lastname  AS 'lastname',

COALESCE(mr.rating, 0)  AS 'answer_rating'

FROM mdl_forum_discussions mfd 

JOIN mdl_forum_posts mfp ON mfd.id=mfp.discussion

JOIN mdl_course mcc ON mfd.course=mcc.id

JOIN mdl_user mus ON mus.id=mfp.userid

JOIN mdl_forum mfm ON mfm.id=mfd.forum

LEFT JOIN mdl_rating mr ON mfp.id=mr.itemid