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, 832, 829, 828, 817, 816, 787, 819, 
    781, 760, 758, 752, 751, 750, 749, 747, 
    732, 731, 725, 724, 723, 717, 707, 673, 
    650, 647, 645, 644, 641, 639, 636, 624, 
    618, 616, 210, 197, 155, 51
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00049

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "26.61"
    },
    "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": "range",
            "possible_keys": [
              "object_id"
            ],
            "key": "object_id",
            "used_key_parts": [
              "object_id",
              "object_type"
            ],
            "key_length": "6",
            "rows_examined_per_scan": 38,
            "rows_produced_per_join": 38,
            "filtered": "100.00",
            "index_condition": "((`betaatif_store`.`cscart_discussion`.`object_id` in (846,832,829,828,817,816,787,819,781,760,758,752,751,750,749,747,732,731,725,724,723,717,707,673,650,647,645,644,641,639,636,624,618,616,210,197,155,51)) and (`betaatif_store`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "22.81",
              "eval_cost": "3.80",
              "prefix_cost": "26.61",
              "data_read_per_join": "912"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        }
      ]
    }
  }
}