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 (
    846, 845, 844, 832, 829, 828, 822, 817, 
    816, 662, 814, 806, 805, 804, 803, 802, 
    801, 800, 799, 798, 797, 796, 795, 792, 
    787, 786, 782, 819, 781, 765, 764, 763, 
    762, 760, 758, 752, 751, 750, 749, 747, 
    744, 743, 742, 741, 732, 731, 727, 725, 
    724, 723, 809, 810, 720, 718, 717, 716, 
    715, 713, 709, 708, 707, 705, 701, 697, 
    696, 695, 693, 682, 676, 673, 671, 670, 
    664, 663, 658, 657, 656, 651, 650, 647, 
    645, 644, 641, 639, 636, 624, 622, 620, 
    619, 618, 616, 615, 608, 607, 600, 377
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00192

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "44.55"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_discussion_posts",
            "access_type": "system",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "rows_examined_per_scan": 0,
            "rows_produced_per_join": 1,
            "filtered": "0.00",
            "const_row_not_found": true,
            "cost_info": {
              "read_cost": "0.00",
              "eval_cost": "0.10",
              "prefix_cost": "0.00",
              "data_read_per_join": "448"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_rating",
            "access_type": "system",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "rows_examined_per_scan": 0,
            "rows_produced_per_join": 1,
            "filtered": "0.00",
            "const_row_not_found": true,
            "cost_info": {
              "read_cost": "0.00",
              "eval_cost": "0.10",
              "prefix_cost": "0.00",
              "data_read_per_join": "16"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion",
            "access_type": "index",
            "possible_keys": [
              "object_id"
            ],
            "key": "object_id",
            "used_key_parts": [
              "object_id",
              "object_type"
            ],
            "key_length": "6",
            "rows_examined_per_scan": 436,
            "rows_produced_per_join": 96,
            "filtered": "22.02",
            "cost_info": {
              "read_cost": "34.95",
              "eval_cost": "9.60",
              "prefix_cost": "44.55",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ],
            "attached_condition": "((`betaatif_store`.`cscart_discussion`.`object_id` in (846,845,844,832,829,828,822,817,816,662,814,806,805,804,803,802,801,800,799,798,797,796,795,792,787,786,782,819,781,765,764,763,762,760,758,752,751,750,749,747,744,743,742,741,732,731,727,725,724,723,809,810,720,718,717,716,715,713,709,708,707,705,701,697,696,695,693,682,676,673,671,670,664,663,658,657,656,651,650,647,645,644,641,639,636,624,622,620,619,618,616,615,608,607,600,377)) and (`betaatif_store`.`cscart_discussion`.`object_type` = 'P'))"
          }
        }
      ]
    }
  }
}