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 (
    88066, 88075, 88082, 87958, 89982, 89983, 
    89984, 88046, 88045, 87987, 87997, 
    88026, 88047, 88048, 88050, 88051, 
    87937, 87950, 87952, 88004, 87948, 
    88029, 93794, 94496, 94499, 94501, 
    94515, 94581, 94843, 94850, 94852, 
    95309, 95316, 95376, 95762, 95778, 
    95779, 95823, 96119, 96508, 96530, 
    96570, 96572, 97620, 97623, 97625, 
    97639, 97705, 99111, 99122, 99124, 
    99126, 99129, 99163, 99172, 99178, 
    99184, 99204, 99207, 99223, 99224, 
    99225, 99226, 99228, 99229, 99244, 
    99253, 99260, 99271, 99280, 99281, 
    100388, 100389, 100432, 100671, 100672, 
    100673
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00151

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "88.81"
    },
    "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": 77,
            "rows_produced_per_join": 77,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (88066,88075,88082,87958,89982,89983,89984,88046,88045,87987,87997,88026,88047,88048,88050,88051,87937,87950,87952,88004,87948,88029,93794,94496,94499,94501,94515,94581,94843,94850,94852,95309,95316,95376,95762,95778,95779,95823,96119,96508,96530,96570,96572,97620,97623,97625,97639,97705,99111,99122,99124,99126,99129,99163,99172,99178,99184,99204,99207,99223,99224,99225,99226,99228,99229,99244,99253,99260,99271,99280,99281,100388,100389,100432,100671,100672,100673)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "46.21",
              "eval_cost": "7.70",
              "prefix_cost": "53.91",
              "data_read_per_join": "1K"
            },
            "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": 77,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "19.25",
              "eval_cost": "7.70",
              "prefix_cost": "80.86",
              "data_read_per_join": "33K"
            },
            "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": 77,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "7.70",
              "prefix_cost": "88.81",
              "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)"
          }
        }
      ]
    }
  }
}