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 (
    507, 7925, 3554, 3552, 3553, 3447, 4214, 
    4554, 3446, 4604, 7603, 7604, 7605, 
    7606, 4059, 3865, 4054, 4058, 4052, 
    4056, 4053, 3870, 3872, 3871, 3873, 
    3862, 262, 1785, 866, 3676, 3677, 323, 
    865, 864, 322, 324, 5071, 6426, 6428, 
    6429, 6427, 5615, 5613, 5614, 5611, 
    5612, 5692, 5693
  ) 
  AND cscart_discussion.object_type = "P" 
  AND cscart_discussion.company_id = 1 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00068

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "67.21"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_discussion",
            "access_type": "range",
            "possible_keys": [
              "object_id",
              "company_id"
            ],
            "key": "object_id",
            "used_key_parts": [
              "object_id",
              "object_type",
              "company_id"
            ],
            "key_length": "10",
            "rows_examined_per_scan": 48,
            "rows_produced_per_join": 48,
            "filtered": "100.00",
            "index_condition": "((`dbggbern`.`cscart_discussion`.`company_id` = 1) and (`dbggbern`.`cscart_discussion`.`object_id` in (507,7925,3554,3552,3553,3447,4214,4554,3446,4604,7603,7604,7605,7606,4059,3865,4054,4058,4052,4056,4053,3870,3872,3871,3873,3862,262,1785,866,3676,3677,323,865,864,322,324,5071,6426,6428,6429,6427,5615,5613,5614,5611,5612,5692,5693)) and (`dbggbern`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "28.81",
              "eval_cost": "4.80",
              "prefix_cost": "33.61",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type",
              "company_id"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_posts",
            "access_type": "ref",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "key": "thread_id",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "dbggbern.cscart_discussion.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 48,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "12.00",
              "eval_cost": "4.80",
              "prefix_cost": "50.41",
              "data_read_per_join": "21K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_posts), (`dbggbern`.`cscart_discussion_posts`.`status` = 'A'), true)"
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_rating",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "post_id"
            ],
            "key_length": "3",
            "ref": [
              "dbggbern.cscart_discussion_posts.post_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 48,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "12.00",
              "eval_cost": "4.80",
              "prefix_cost": "67.21",
              "data_read_per_join": "768"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_rating), ((`dbggbern`.`cscart_discussion_rating`.`thread_id` = `dbggbern`.`cscart_discussion`.`thread_id`) and (`dbggbern`.`cscart_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}