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 (
    97865, 97866, 97869, 97870, 97873, 97903, 
    97904, 97905, 97906, 97907, 97908, 
    97909, 97910, 97935, 97936, 97937, 
    97938, 97939, 97940, 97941, 97942, 
    97952, 97962, 97963, 97967, 97970, 
    97971, 97972, 97973, 97975, 97978, 
    97979, 97982, 97983, 97986, 97987, 
    98041, 98043, 98045, 98047, 98049, 
    98051, 98084, 98122, 98123, 98124, 
    98125, 98126, 98127, 98128, 98129, 
    98169, 98171, 98172, 98174, 98327, 
    98328, 98329, 98330, 98331, 98332, 
    98333, 98334, 98335, 98336, 98337, 
    98338, 98339, 98340, 98341, 98342, 
    98367, 98368, 98369, 98370, 98371, 
    98372, 98373, 98374, 98375, 98376, 
    98377, 98378, 98379, 98380, 98381, 
    98382, 98418, 98420, 98551, 98571, 
    98683, 98684, 98717, 98719, 98721
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00131

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 (97865,97866,97869,97870,97873,97903,97904,97905,97906,97907,97908,97909,97910,97935,97936,97937,97938,97939,97940,97941,97942,97952,97962,97963,97967,97970,97971,97972,97973,97975,97978,97979,97982,97983,97986,97987,98041,98043,98045,98047,98049,98051,98084,98122,98123,98124,98125,98126,98127,98128,98129,98169,98171,98172,98174,98327,98328,98329,98330,98331,98332,98333,98334,98335,98336,98337,98338,98339,98340,98341,98342,98367,98368,98369,98370,98371,98372,98373,98374,98375,98376,98377,98378,98379,98380,98381,98382,98418,98420,98551,98571,98683,98684,98717,98719,98721)) 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_2",
            "used_key_parts": [
              "thread_id",
              "status"
            ],
            "key_length": "6",
            "ref": [
              "nuie_scalesta_net.cscart_discussion.thread_id",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "using_index": true,
            "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"
            ]
          }
        },
        {
          "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)"
          }
        }
      ]
    }
  }
}