SELECT 
  q_discussion.object_id AS product_id, 
  AVG(
    q_discussion_rating.rating_value
  ) AS average_rating, 
  q_discussion.type AS discussion_type, 
  q_discussion.thread_id AS discussion_thread_id 
FROM 
  q_discussion 
  LEFT JOIN q_discussion_posts ON q_discussion_posts.thread_id = q_discussion.thread_id 
  AND q_discussion_posts.status = "A" 
  LEFT JOIN q_discussion_rating ON q_discussion.thread_id = q_discussion_rating.thread_id 
  AND q_discussion_rating.post_id = q_discussion_posts.post_id 
  AND q_discussion_rating.rating_value != 0 
WHERE 
  q_discussion.object_id IN (
    6415, 6416, 6417, 6418, 6419, 6420, 6421, 
    6422, 6423, 6424, 6425, 6426, 6427, 
    6428, 6429, 6430, 6431, 6432, 6433, 
    6434, 6435, 6436, 6437, 6438, 6439, 
    6440, 6441, 6442, 6443, 6444, 6445, 
    6446, 6447, 6448, 6449, 6450, 6451, 
    6452, 6453, 6454, 6456, 6457, 6458, 
    6459, 6460, 6461, 6462, 6463, 6464, 
    6465, 6466, 6467, 6468, 6469, 6470, 
    6471, 6472, 6473, 6474, 6475, 6476, 
    6477, 6478, 6479
  ) 
  AND q_discussion.object_type = "P" 
GROUP BY 
  q_discussion.object_id

Query time 0.00081

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "460.81"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "q_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": 64,
            "rows_produced_per_join": 64,
            "filtered": "100.00",
            "index_condition": "((`portal`.`q_discussion`.`object_id` in (6415,6416,6417,6418,6419,6420,6421,6422,6423,6424,6425,6426,6427,6428,6429,6430,6431,6432,6433,6434,6435,6436,6437,6438,6439,6440,6441,6442,6443,6444,6445,6446,6447,6448,6449,6450,6451,6452,6453,6454,6456,6457,6458,6459,6460,6461,6462,6463,6464,6465,6466,6467,6468,6469,6470,6471,6472,6473,6474,6475,6476,6477,6478,6479)) and (`portal`.`q_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "140.81",
              "eval_cost": "12.80",
              "prefix_cost": "153.61",
              "data_read_per_join": "1024"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        },
        {
          "table": {
            "table_name": "q_discussion_posts",
            "access_type": "ref",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "key": "thread_id",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.q_discussion.thread_id"
            ],
            "rows_examined_per_scan": 2,
            "rows_produced_per_join": 128,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "128.00",
              "eval_cost": "25.60",
              "prefix_cost": "307.21",
              "data_read_per_join": "56K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(q_discussion_posts), (`portal`.`q_discussion_posts`.`status` = 'A'), true)"
          }
        },
        {
          "table": {
            "table_name": "q_discussion_rating",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "post_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.q_discussion_posts.post_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 128,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "128.00",
              "eval_cost": "25.60",
              "prefix_cost": "460.81",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(q_discussion_rating), ((`portal`.`q_discussion_rating`.`thread_id` = `portal`.`q_discussion`.`thread_id`) and (`portal`.`q_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}