SELECT 
  cscart_discussion.object_id AS product_id, 
  AVG(
    cscart_discussion_rating.rating_value
  ) AS average_rating, 
  cscart_discussion.type AS discussion_type, 
  cscart_discussion.thread_id AS discussion_thread_id 
FROM 
  cscart_discussion 
  LEFT JOIN cscart_discussion_posts ON cscart_discussion_posts.thread_id = cscart_discussion.thread_id 
  AND cscart_discussion_posts.status = "A" 
  LEFT JOIN cscart_discussion_rating ON cscart_discussion.thread_id = cscart_discussion_rating.thread_id 
  AND cscart_discussion_rating.post_id = cscart_discussion_posts.post_id 
  AND cscart_discussion_rating.rating_value != 0 
WHERE 
  cscart_discussion.object_id IN (
    85974, 85975, 85977, 85978, 85979, 85980, 
    85981, 85982, 85983, 85984, 85985, 
    85986, 85987, 85988, 85989, 85990, 
    85991, 85992, 85993, 85994, 85995, 
    85996, 85997, 85998, 85999, 86003, 
    86004, 86005, 86006, 86007, 86008, 
    86009, 86010, 86011, 86012, 86014, 
    86015, 86017, 86018, 86019, 86020, 
    86021, 86022, 86023, 86024, 86025, 
    86026, 86027, 86028, 86029, 86030, 
    86031, 86032, 86033, 86034, 86035, 
    86036, 86037, 86038, 86039, 86040, 
    86041, 86042, 86043, 86044, 86045, 
    86046, 86047, 86048, 86049, 86050, 
    86051, 86052, 86053, 86054, 86055, 
    86056, 86057, 86058, 86059, 86060, 
    86062, 86064, 86065, 86066, 86068
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00127

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "99.16"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_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": 86,
            "rows_produced_per_join": 86,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (85974,85975,85977,85978,85979,85980,85981,85982,85983,85984,85985,85986,85987,85988,85989,85990,85991,85992,85993,85994,85995,85996,85997,85998,85999,86003,86004,86005,86006,86007,86008,86009,86010,86011,86012,86014,86015,86017,86018,86019,86020,86021,86022,86023,86024,86025,86026,86027,86028,86029,86030,86031,86032,86033,86034,86035,86036,86037,86038,86039,86040,86041,86042,86043,86044,86045,86046,86047,86048,86049,86050,86051,86052,86053,86054,86055,86056,86057,86058,86059,86060,86062,86064,86065,86066,86068)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "51.61",
              "eval_cost": "8.60",
              "prefix_cost": "60.21",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_posts",
            "access_type": "ref",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "key": "thread_id",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "nuie_scalesta_net.cscart_discussion.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 86,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "21.50",
              "eval_cost": "8.60",
              "prefix_cost": "90.31",
              "data_read_per_join": "37K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_posts), (`nuie_scalesta_net`.`cscart_discussion_posts`.`status` = 'A'), true)"
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_rating",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 86,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "8.60",
              "prefix_cost": "99.16",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_rating), ((`nuie_scalesta_net`.`cscart_discussion_rating`.`post_id` = `nuie_scalesta_net`.`cscart_discussion_posts`.`post_id`) and (`nuie_scalesta_net`.`cscart_discussion_rating`.`thread_id` = `nuie_scalesta_net`.`cscart_discussion`.`thread_id`) and (`nuie_scalesta_net`.`cscart_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}