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 (
    32517, 32518, 32520, 32522, 32523, 32524, 
    32525, 32526, 32527, 32528, 32529, 
    32530, 32532, 32533, 32534, 32535, 
    32537, 32538, 32539, 32540, 32541, 
    32542, 32543, 32544, 32545, 32546, 
    32548, 32549, 32550, 32551, 32552, 
    32553
  ) 
  AND q_discussion.object_type = "P" 
GROUP BY 
  q_discussion.object_id

Query time 0.00074

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "230.41"
    },
    "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": 32,
            "rows_produced_per_join": 32,
            "filtered": "100.00",
            "index_condition": "((`portal`.`q_discussion`.`object_id` in (32517,32518,32520,32522,32523,32524,32525,32526,32527,32528,32529,32530,32532,32533,32534,32535,32537,32538,32539,32540,32541,32542,32543,32544,32545,32546,32548,32549,32550,32551,32552,32553)) and (`portal`.`q_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "70.41",
              "eval_cost": "6.40",
              "prefix_cost": "76.81",
              "data_read_per_join": "512"
            },
            "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": 64,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "64.00",
              "eval_cost": "12.80",
              "prefix_cost": "153.61",
              "data_read_per_join": "28K"
            },
            "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": 64,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "64.00",
              "eval_cost": "12.80",
              "prefix_cost": "230.41",
              "data_read_per_join": "1024"
            },
            "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)"
          }
        }
      ]
    }
  }
}