SELECT 
  cscart_discussion.object_id AS product_id, 
  AVG(
    cscart_discussion_rating.rating_value
  ) AS average_rating, 
  cscart_discussion.type AS discussion_type, 
  cscart_discussion.thread_id AS discussion_thread_id 
FROM 
  cscart_discussion 
  LEFT JOIN cscart_discussion_posts ON cscart_discussion_posts.thread_id = cscart_discussion.thread_id 
  AND cscart_discussion_posts.status = "A" 
  LEFT JOIN cscart_discussion_rating ON cscart_discussion.thread_id = cscart_discussion_rating.thread_id 
  AND cscart_discussion_rating.post_id = cscart_discussion_posts.post_id 
  AND cscart_discussion_rating.rating_value != 0 
WHERE 
  cscart_discussion.object_id IN (
    8303, 8665, 9880, 8281, 8286, 9818, 9883, 
    8666, 8300, 8306, 8289, 8361
  ) 
  AND cscart_discussion.object_type = "P" 
  AND cscart_discussion.company_id = 2 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00049

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_discussion range object_id,company_id object_id 10 12 Using index condition
1 SIMPLE cscart_discussion_posts ref thread_id,thread_id_2 thread_id 3 mahm3t_cs443.cscart_discussion.thread_id 4 Using where
1 SIMPLE cscart_discussion_rating eq_ref PRIMARY,thread_id PRIMARY 3 mahm3t_cs443.cscart_discussion_posts.post_id 1 Using where

Result

product_id average_rating discussion_type discussion_thread_id
8281 B 3987
8286 B 3329
8289 B 1062
8300 5.0000 B 3995
8303 B 3997
8306 B 4006
8361 5.0000 B 4007
8665 B 1215
8666 B 1216
9818 B 3154
9880 B 4148
9883 B 4151