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 (
    85896, 85897, 85902, 85884, 85903, 85885, 
    85899, 85890, 85898, 85891, 85905, 
    85887, 85904, 85886, 85893, 85895, 
    85892, 85901, 85883, 85889, 85879, 
    85880, 85874, 85875, 85881, 85876, 
    85878, 85873, 85877, 85872, 85914, 
    85915, 85919, 85946, 85947, 85912, 
    85945, 85926, 85923, 85928, 85921, 
    85943, 85944, 85942, 85937, 85938, 
    85936, 85934, 85935, 85940, 85941, 
    85933, 85939, 85959, 85957, 85931, 
    85932, 85930, 85954, 85953, 85950, 
    85951, 85948, 85909, 84692, 85910, 
    85911, 84957, 85906, 85907, 84852, 
    84751, 87975, 85908, 84753, 84860, 
    84863, 92922, 92923, 92924, 92925, 
    92926, 92927, 92928, 92929, 92930, 
    92931, 92932, 92933
  ) 
  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": "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 (85896,85897,85902,85884,85903,85885,85899,85890,85898,85891,85905,85887,85904,85886,85893,85895,85892,85901,85883,85889,85879,85880,85874,85875,85881,85876,85878,85873,85877,85872,85914,85915,85919,85946,85947,85912,85945,85926,85923,85928,85921,85943,85944,85942,85937,85938,85936,85934,85935,85940,85941,85933,85939,85959,85957,85931,85932,85930,85954,85953,85950,85951,85948,85909,84692,85910,85911,84957,85906,85907,84852,84751,87975,85908,84753,84860,84863,92922,92923,92924,92925,92926,92927,92928,92929,92930,92931,92932,92933)) 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)"
          }
        }
      ]
    }
  }
}