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 (
    85091, 85092, 85177, 85178, 85223, 85224, 
    85269, 85270, 85105, 89812, 89813, 
    89864, 89865, 89936, 89937, 91502, 
    91503, 89772, 85300, 85301, 85397, 
    85398, 85448, 85449, 85499, 85500, 
    85131, 85132, 83580, 85346, 85347, 
    85068, 85154, 85200, 85246, 89827, 
    89879, 89951, 91517, 83566, 85108, 
    86517, 86518, 86793, 86794, 82837, 
    82910, 82983, 83397, 83407, 86140, 
    86163, 86648, 86717, 83448, 83453, 
    89760, 89761, 89811, 89863, 89935, 
    91501, 85299, 85396, 85447, 85498, 
    85328, 85329, 85425, 85426, 85476, 
    85477, 85527, 85528, 85090, 85176, 
    85222, 85268, 85345, 83066, 83067, 
    83619, 83620, 89775, 90902, 90903, 
    90981, 90982, 82611, 85374, 85375, 
    82638, 83535, 85130, 89814, 89866
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00188

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "110.66"
    },
    "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": 96,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (85091,85092,85177,85178,85223,85224,85269,85270,85105,89812,89813,89864,89865,89936,89937,91502,91503,89772,85300,85301,85397,85398,85448,85449,85499,85500,85131,85132,83580,85346,85347,85068,85154,85200,85246,89827,89879,89951,91517,83566,85108,86517,86518,86793,86794,82837,82910,82983,83397,83407,86140,86163,86648,86717,83448,83453,89760,89761,89811,89863,89935,91501,85299,85396,85447,85498,85328,85329,85425,85426,85476,85477,85527,85528,85090,85176,85222,85268,85345,83066,83067,83619,83620,89775,90902,90903,90981,90982,82611,85374,85375,82638,83535,85130,89814,89866)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "57.61",
              "eval_cost": "9.60",
              "prefix_cost": "67.21",
              "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": 96,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "24.00",
              "eval_cost": "9.60",
              "prefix_cost": "100.81",
              "data_read_per_join": "42K"
            },
            "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": 96,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "9.60",
              "prefix_cost": "110.66",
              "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)"
          }
        }
      ]
    }
  }
}