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 (
    88304, 88305, 89712, 89713, 88302, 88303, 
    89708, 89709, 89710, 89711, 88300, 
    88301, 89706, 89707, 89701, 89702, 
    88296, 88297, 89699, 89700, 88381, 
    88382, 88377, 88378, 88379, 88380, 
    88375, 88376, 88370, 88371, 88368, 
    88369, 94387, 94396, 94397, 94399, 
    94400, 94423, 94424, 94858, 94859, 
    94867, 94868, 94870, 94871, 94896, 
    94897, 94906, 94907, 94916, 94917, 
    94919, 94920, 94945, 94946, 96250, 
    96251, 96260, 96261, 96263, 96264, 
    96290, 96291, 96576, 96581, 96598, 
    96599, 100550, 100559, 100560, 100562, 
    100563, 100589, 100590, 101579, 101580, 
    101589, 101590, 101592, 101593, 101619, 
    101620, 101624
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00169

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "95.71"
    },
    "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": 83,
            "rows_produced_per_join": 83,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (88304,88305,89712,89713,88302,88303,89708,89709,89710,89711,88300,88301,89706,89707,89701,89702,88296,88297,89699,89700,88381,88382,88377,88378,88379,88380,88375,88376,88370,88371,88368,88369,94387,94396,94397,94399,94400,94423,94424,94858,94859,94867,94868,94870,94871,94896,94897,94906,94907,94916,94917,94919,94920,94945,94946,96250,96251,96260,96261,96263,96264,96290,96291,96576,96581,96598,96599,100550,100559,100560,100562,100563,100589,100590,101579,101580,101589,101590,101592,101593,101619,101620,101624)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "49.81",
              "eval_cost": "8.30",
              "prefix_cost": "58.11",
              "data_read_per_join": "1K"
            },
            "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": 83,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "20.75",
              "eval_cost": "8.30",
              "prefix_cost": "87.16",
              "data_read_per_join": "36K"
            },
            "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": 83,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "8.30",
              "prefix_cost": "95.71",
              "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)"
          }
        }
      ]
    }
  }
}