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 (
    97657, 97658, 97659, 97660, 97661, 97662, 
    97663, 97664, 97665, 97666, 97667, 
    97668, 97669, 97670, 97671, 97672, 
    97673, 97674, 97675, 97676, 97677, 
    97678, 97679, 97680, 97681, 97682, 
    97683, 97684, 97685, 97686, 97687, 
    97688, 97689, 97690, 97691, 97692, 
    97693, 97694, 97695, 97696, 97697, 
    97698, 97699, 97700, 97701, 97702, 
    97703, 97704, 97705, 97706, 97707, 
    97708, 97709, 97710, 97711, 97712, 
    98054, 98055, 98056, 98057, 98058, 
    98059, 98060, 98061, 98062, 98063, 
    98064, 98065, 98066, 98067, 98068, 
    98069, 98070, 98071, 98072, 98073, 
    98074, 98075, 98076, 98077, 98078, 
    98079, 98080, 98081, 98082, 98083, 
    98523, 98524, 98525, 98526, 98527, 
    98528, 98529, 98530, 98531, 98532
  ) 
  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": "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 (97657,97658,97659,97660,97661,97662,97663,97664,97665,97666,97667,97668,97669,97670,97671,97672,97673,97674,97675,97676,97677,97678,97679,97680,97681,97682,97683,97684,97685,97686,97687,97688,97689,97690,97691,97692,97693,97694,97695,97696,97697,97698,97699,97700,97701,97702,97703,97704,97705,97706,97707,97708,97709,97710,97711,97712,98054,98055,98056,98057,98058,98059,98060,98061,98062,98063,98064,98065,98066,98067,98068,98069,98070,98071,98072,98073,98074,98075,98076,98077,98078,98079,98080,98081,98082,98083,98523,98524,98525,98526,98527,98528,98529,98530,98531,98532)) 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)"
          }
        }
      ]
    }
  }
}