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 (
    13547, 18032, 18031, 18030, 12900, 11591, 
    18056, 8034, 7666, 8257, 8063, 10729, 
    10697, 7714, 7625, 11585, 8733, 7481, 
    8120, 10998, 7279, 13244, 7655, 7633
  ) 
  AND cscart_discussion.object_type = "P" 
  AND cscart_discussion.company_id = 1 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00092

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_discussion",
          "access_type": "range",
          "possible_keys": ["object_id", "idx_company_id"],
          "key": "object_id",
          "key_length": "10",
          "used_key_parts": ["object_id", "object_type", "company_id"],
          "rows": 24,
          "filtered": 100,
          "index_condition": "cscart_discussion.company_id = 1 and cscart_discussion.object_id in (13547,18032,18031,18030,12900,11591,18056,8034,7666,8257,8063,10729,10697,7714,7625,11585,8733,7481,8120,10998,7279,13244,7655,7633) and cscart_discussion.object_type = 'P'"
        }
      },
      {
        "table": {
          "table_name": "cscart_discussion_posts",
          "access_type": "ref",
          "possible_keys": ["thread_id", "thread_id_2"],
          "key": "thread_id_2",
          "key_length": "6",
          "used_key_parts": ["thread_id", "status"],
          "ref": ["lillyshop_lillyshop.cscart_discussion.thread_id", "const"],
          "rows": 2,
          "filtered": 100,
          "attached_condition": "trigcond(cscart_discussion_posts.`status` = 'A')"
        }
      },
      {
        "table": {
          "table_name": "cscart_discussion_rating",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "thread_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["post_id"],
          "ref": ["lillyshop_lillyshop.cscart_discussion_posts.post_id"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(cscart_discussion_rating.thread_id = cscart_discussion.thread_id and cscart_discussion_rating.rating_value <> 0 and trigcond(cscart_discussion_posts.post_id is not null))"
        }
      }
    ]
  }
}

Result

product_id average_rating discussion_type discussion_thread_id
7279 B 7860
7481 B 8084
7625 B 8239
7633 B 8251
7655 B 8275
7666 B 8287
7714 B 8336
8034 B 8679
8063 B 8708
8120 B 8767
8257 B 8908
8733 B 9404
10697 B 11413
10729 B 11445
10998 B 11716
11585 B 12323
11591 B 12329
12900 B 13659
13244 B 14010
13547 B 14321
18030 D 18828
18031 D 18829
18032 D 18830
18056 D 18855