SELECT 
  discussion.object_id AS product_id, 
  AVG(discussion_rating.rating_value) AS average_rating, 
  discussion.type AS discussion_type, 
  discussion.thread_id AS discussion_thread_id 
FROM 
  discussion 
  LEFT JOIN discussion_posts ON discussion_posts.thread_id = discussion.thread_id 
  AND discussion_posts.status = "A" 
  LEFT JOIN discussion_rating ON discussion.thread_id = discussion_rating.thread_id 
  AND discussion_rating.post_id = discussion_posts.post_id 
  AND discussion_rating.rating_value != 0 
WHERE 
  discussion.object_id IN (
    283106, 283123, 283129, 289266, 291486, 
    306655, 282371, 282946, 282977, 282989, 
    283048, 283058, 283139, 289286, 289289, 
    289300, 282362, 282379, 282895, 282912, 
    282922, 282959, 283047, 283086, 291454, 
    282370, 282934, 282944, 282951, 282964, 
    283003, 283005, 283019, 283031, 283071, 
    283075, 283135, 283137, 283154, 289293, 
    291446, 291500, 282353, 282366, 282369, 
    282916, 282937, 282950, 282962, 282978, 
    283028, 283045, 283073, 283078, 283104, 
    283110, 283127, 283153, 289261, 282372, 
    282906, 282945, 282970, 282986, 283059, 
    283112, 283147, 283155, 289215, 289284, 
    291448, 291481, 282896, 282919, 283027, 
    283092, 283102, 283133, 291461, 291496, 
    306662, 282355, 282374, 282902, 282967, 
    282995, 282996, 283036, 283130, 289269, 
    291447, 291489, 282367, 282894, 282981, 
    283008
  ) 
  AND discussion.object_type = "P" 
GROUP BY 
  discussion.object_id

Query time 0.00324

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "257.02"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "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": "((`goimagine`.`discussion`.`object_id` in (283106,283123,283129,289266,291486,306655,282371,282946,282977,282989,283048,283058,283139,289286,289289,289300,282362,282379,282895,282912,282922,282959,283047,283086,291454,282370,282934,282944,282951,282964,283003,283005,283019,283031,283071,283075,283135,283137,283154,289293,291446,291500,282353,282366,282369,282916,282937,282950,282962,282978,283028,283045,283073,283078,283104,283110,283127,283153,289261,282372,282906,282945,282970,282986,283059,283112,283147,283155,289215,289284,291448,291481,282896,282919,283027,283092,283102,283133,291461,291496,306662,282355,282374,282902,282967,282995,282996,283036,283130,289269,291447,291489,282367,282894,282981,283008)) and (`goimagine`.`discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "147.47",
              "eval_cost": "9.60",
              "prefix_cost": "157.07",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        },
        {
          "table": {
            "table_name": "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": [
              "goimagine.discussion.thread_id",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 168,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "24.02",
              "eval_cost": "16.87",
              "prefix_cost": "197.96",
              "data_read_per_join": "73K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ]
          }
        },
        {
          "table": {
            "table_name": "discussion_rating",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "post_id"
            ],
            "key_length": "3",
            "ref": [
              "goimagine.discussion_posts.post_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 168,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "42.19",
              "eval_cost": "16.87",
              "prefix_cost": "257.03",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(discussion_rating), ((`goimagine`.`discussion_rating`.`thread_id` = `goimagine`.`discussion`.`thread_id`) and (`goimagine`.`discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}