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 (
    47544, 47645, 47646, 47649, 47651, 47652, 
    47656, 47660, 47676, 47677, 47678, 
    47686, 47690, 47692, 47693, 47697, 
    47698, 47699, 47700, 47701, 47703, 
    47771
  ) 
  AND q_discussion.object_type = "P" 
GROUP BY 
  q_discussion.object_id

Query time 0.00061

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "158.41"
    },
    "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": 22,
            "rows_produced_per_join": 22,
            "filtered": "100.00",
            "index_condition": "((`portal`.`q_discussion`.`object_id` in (47544,47645,47646,47649,47651,47652,47656,47660,47676,47677,47678,47686,47690,47692,47693,47697,47698,47699,47700,47701,47703,47771)) and (`portal`.`q_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "48.41",
              "eval_cost": "4.40",
              "prefix_cost": "52.81",
              "data_read_per_join": "352"
            },
            "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": 44,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "44.00",
              "eval_cost": "8.80",
              "prefix_cost": "105.61",
              "data_read_per_join": "19K"
            },
            "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": 44,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "44.00",
              "eval_cost": "8.80",
              "prefix_cost": "158.41",
              "data_read_per_join": "704"
            },
            "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)"
          }
        }
      ]
    }
  }
}