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 (
    20090, 20091, 20092, 20093, 20094, 18661, 
    18662, 19131, 18664, 20724, 20725, 
    20728, 20955, 20956, 20957, 20958, 
    20959, 22277, 20971, 21078, 21102, 
    20972, 20973, 20974
  ) 
  AND cscart_discussion.object_type = "P" 
  AND cscart_discussion.company_id = 1 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00138

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 (20090,20091,20092,20093,20094,18661,18662,19131,18664,20724,20725,20728,20955,20956,20957,20958,20959,22277,20971,21078,21102,20972,20973,20974) 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
18661 D 19511
18662 D 19512
18664 D 19514
19131 D 20021
20090 D 21124
20091 D 21125
20092 D 21126
20093 D 21127
20094 D 21128
20724 D 21796
20725 D 21797
20728 D 21800
20955 D 22032
20956 D 22033
20957 D 22034
20958 D 22035
20959 D 22036
20971 D 22049
20972 D 22050
20973 D 22051
20974 D 22052
21078 D 22157
21102 D 22197
22277 D 23506