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 (
    223931, 223968, 224015, 223958, 223988, 
    223974, 223967, 223981, 224021, 223935, 
    224043, 224018, 223964, 223955, 224023, 
    223949, 223998, 223962, 223934, 223977, 
    224011, 223996, 223994, 223975, 224024, 
    223932, 223952, 224014, 224026, 223970, 
    224013, 223963, 224042, 223933, 223937, 
    223971, 223954, 223960, 223987, 223984, 
    223966, 223978, 223993, 224027, 223948, 
    224036, 224038, 224046
  ) 
  AND discussion.object_type = "P" 
GROUP BY 
  discussion.object_id

Query time 0.00186

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "113.12"
    },
    "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": 48,
            "rows_produced_per_join": 48,
            "filtered": "100.00",
            "index_condition": "((`goimagine`.`discussion`.`object_id` in (223931,223968,224015,223958,223988,223974,223967,223981,224021,223935,224043,224018,223964,223955,224023,223949,223998,223962,223934,223977,224011,223996,223994,223975,224024,223932,223952,224014,224026,223970,224013,223963,224042,223933,223937,223971,223954,223960,223987,223984,223966,223978,223993,224027,223948,224036,224038,224046)) and (`goimagine`.`discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "58.34",
              "eval_cost": "4.80",
              "prefix_cost": "63.14",
              "data_read_per_join": "1K"
            },
            "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": 84,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "12.01",
              "eval_cost": "8.44",
              "prefix_cost": "83.59",
              "data_read_per_join": "36K"
            },
            "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": 84,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "21.09",
              "eval_cost": "8.44",
              "prefix_cost": "113.12",
              "data_read_per_join": "1K"
            },
            "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)"
          }
        }
      ]
    }
  }
}