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 (
    82485, 89533, 85606, 85605, 89532, 93902, 
    93903, 93904, 93905, 93906, 93910, 
    93911, 93912, 94965, 94966, 94967, 
    94968, 94969, 94970, 94971, 94972, 
    94973, 94974, 94975, 94976, 94977, 
    94978, 94979, 94980, 94981, 94982, 
    95450, 95459, 95463, 95511, 95512, 
    95513, 95517, 95518, 95519, 95527, 
    95528, 95542, 95543, 95544, 96792, 
    96848, 96849, 96850, 96851, 96852, 
    96853, 96854, 96855, 96856, 96857, 
    96858, 96859, 96860, 96861, 96862, 
    96863, 96864, 96865, 98509, 98510, 
    100187, 100188, 100189, 100190, 100191, 
    100195, 100196, 100197, 100298, 100300
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00139

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "87.66"
    },
    "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": 76,
            "rows_produced_per_join": 76,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (82485,89533,85606,85605,89532,93902,93903,93904,93905,93906,93910,93911,93912,94965,94966,94967,94968,94969,94970,94971,94972,94973,94974,94975,94976,94977,94978,94979,94980,94981,94982,95450,95459,95463,95511,95512,95513,95517,95518,95519,95527,95528,95542,95543,95544,96792,96848,96849,96850,96851,96852,96853,96854,96855,96856,96857,96858,96859,96860,96861,96862,96863,96864,96865,98509,98510,100187,100188,100189,100190,100191,100195,100196,100197,100298,100300)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "45.61",
              "eval_cost": "7.60",
              "prefix_cost": "53.21",
              "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": 76,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "19.00",
              "eval_cost": "7.60",
              "prefix_cost": "79.81",
              "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": 76,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "7.60",
              "prefix_cost": "87.66",
              "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)"
          }
        }
      ]
    }
  }
}