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 (
    427, 408, 382, 418, 1930, 381, 1529, 1465, 
    329, 439, 393, 394, 396, 383, 440, 327, 
    385, 405, 413, 1937, 414, 389, 426, 442, 
    1936, 326, 322
  ) 
  AND cscart_discussion.object_type = "P" 
  AND cscart_discussion.company_id = 1 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00079

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "129.61"
    },
    "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": 27,
            "rows_produced_per_join": 27,
            "filtered": "100.00",
            "index_condition": "((`eshopuga_upgr_4122`.`cscart_discussion`.`company_id` = 1) and (`eshopuga_upgr_4122`.`cscart_discussion`.`object_id` in (427,408,382,418,1930,381,1529,1465,329,439,393,394,396,383,440,327,385,405,413,1937,414,389,426,442,1936,326,322)) and (`eshopuga_upgr_4122`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "59.41",
              "eval_cost": "5.40",
              "prefix_cost": "64.81",
              "data_read_per_join": "648"
            },
            "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": [
              "eshopuga_upgr_4122.cscart_discussion.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 27,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "27.00",
              "eval_cost": "5.40",
              "prefix_cost": "97.21",
              "data_read_per_join": "11K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_posts), (`eshopuga_upgr_4122`.`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": [
              "eshopuga_upgr_4122.cscart_discussion_posts.post_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 27,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "27.00",
              "eval_cost": "5.40",
              "prefix_cost": "129.61",
              "data_read_per_join": "432"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_rating), ((`eshopuga_upgr_4122`.`cscart_discussion_rating`.`thread_id` = `eshopuga_upgr_4122`.`cscart_discussion`.`thread_id`) and (`eshopuga_upgr_4122`.`cscart_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}