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 (
    85257, 89242, 83071, 83072, 83624, 83625, 
    90907, 90908, 90986, 90987, 85082, 
    85168, 85214, 85260, 83038, 90874, 
    90953, 82622, 85119, 85122, 86189, 
    86212, 86521, 86797, 90564, 90570, 
    90576, 89073, 83069, 83622, 90905, 
    90984, 85080, 85166, 85212, 85258, 
    86193, 86194, 86216, 86217, 86525, 
    86526, 86801, 86802, 84678, 87304, 
    87305, 87316, 87317, 87328, 87329, 
    87340, 87341, 85120, 87310, 87311, 
    87322, 87323, 87334, 87335, 87346, 
    87347, 84654, 84655, 89818, 89819, 
    89870, 89871, 89942, 89943, 91508, 
    91509, 83083, 83084, 83611, 83612, 
    86144, 86145, 86167, 86168, 86660, 
    86661, 86729, 86730, 90922, 90923, 
    91001, 91002, 87298, 87299, 87292, 
    87293, 84527, 84528, 84593, 84594
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00134

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "110.66"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_discussion",
            "access_type": "range",
            "possible_keys": [
              "object_id"
            ],
            "key": "object_id",
            "used_key_parts": [
              "object_id",
              "object_type"
            ],
            "key_length": "6",
            "rows_examined_per_scan": 96,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (85257,89242,83071,83072,83624,83625,90907,90908,90986,90987,85082,85168,85214,85260,83038,90874,90953,82622,85119,85122,86189,86212,86521,86797,90564,90570,90576,89073,83069,83622,90905,90984,85080,85166,85212,85258,86193,86194,86216,86217,86525,86526,86801,86802,84678,87304,87305,87316,87317,87328,87329,87340,87341,85120,87310,87311,87322,87323,87334,87335,87346,87347,84654,84655,89818,89819,89870,89871,89942,89943,91508,91509,83083,83084,83611,83612,86144,86145,86167,86168,86660,86661,86729,86730,90922,90923,91001,91002,87298,87299,87292,87293,84527,84528,84593,84594)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "57.61",
              "eval_cost": "9.60",
              "prefix_cost": "67.21",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        },
        {
          "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": [
              "nuie_scalesta_net.cscart_discussion.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "24.00",
              "eval_cost": "9.60",
              "prefix_cost": "100.81",
              "data_read_per_join": "42K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_posts), (`nuie_scalesta_net`.`cscart_discussion_posts`.`status` = 'A'), true)"
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_rating",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "9.60",
              "prefix_cost": "110.66",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_rating), ((`nuie_scalesta_net`.`cscart_discussion_rating`.`post_id` = `nuie_scalesta_net`.`cscart_discussion_posts`.`post_id`) and (`nuie_scalesta_net`.`cscart_discussion_rating`.`thread_id` = `nuie_scalesta_net`.`cscart_discussion`.`thread_id`) and (`nuie_scalesta_net`.`cscart_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}