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 (
    8306, 8289, 8361, 8304, 9885, 8367, 9882, 
    8288, 8275, 8733, 8362, 8305
  ) 
  AND cscart_discussion.object_type = "P" 
  AND cscart_discussion.company_id = 1 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00072

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
8275 5.0000 B 2455
8288 B 2464
8289 B 2465
8304 5.0000 B 2474
8305 B 2475
8306 B 2476
8361 B 2477
8362 B 2478
8367 1.0000 B 2482
8733 5.0000 B 2935
9882 5.0000 B 3342
9885 5.0000 B 3259