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 (
    95487, 95494, 95495, 95496, 95505, 95506, 
    95509, 95510, 96182, 96183, 96184, 
    96185, 96785, 96786, 96817, 96818, 
    96819, 96820, 96821, 96822, 96823, 
    96824, 96825, 96893, 96894, 96895, 
    96896, 96897, 96898, 96899, 96900, 
    96901, 96902, 96903, 96904, 96905, 
    96906, 96907, 96908, 96909, 96910, 
    96911, 96912, 96913, 96914, 96915, 
    96916, 96969, 96970, 96971, 96972, 
    96973, 96974, 96975, 96976, 96977, 
    96978, 96979, 96980, 98516, 98891, 
    98894, 98895, 98896, 100248, 100249, 
    100250, 100254, 100255, 100256, 100257, 
    100258, 100259, 100328, 100329, 100330, 
    100335, 100336, 100438, 100439, 100440, 
    100441, 100442, 100443, 100444, 101536, 
    101537, 101538, 101539
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00129

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "102.61"
    },
    "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": 89,
            "rows_produced_per_join": 89,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (95487,95494,95495,95496,95505,95506,95509,95510,96182,96183,96184,96185,96785,96786,96817,96818,96819,96820,96821,96822,96823,96824,96825,96893,96894,96895,96896,96897,96898,96899,96900,96901,96902,96903,96904,96905,96906,96907,96908,96909,96910,96911,96912,96913,96914,96915,96916,96969,96970,96971,96972,96973,96974,96975,96976,96977,96978,96979,96980,98516,98891,98894,98895,98896,100248,100249,100250,100254,100255,100256,100257,100258,100259,100328,100329,100330,100335,100336,100438,100439,100440,100441,100442,100443,100444,101536,101537,101538,101539)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "53.41",
              "eval_cost": "8.90",
              "prefix_cost": "62.31",
              "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": 89,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "22.25",
              "eval_cost": "8.90",
              "prefix_cost": "93.46",
              "data_read_per_join": "38K"
            },
            "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": 89,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "8.90",
              "prefix_cost": "102.61",
              "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)"
          }
        }
      ]
    }
  }
}