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 (
    597, 584, 573, 561, 556, 553, 549, 545, 
    541, 525, 521, 517, 513, 507, 497, 492, 
    489, 486, 482, 455, 453, 452, 451, 450, 
    449, 448, 447, 446, 445, 444, 443, 442, 
    394, 378
  ) 
  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": "23.81"
    },
    "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": 34,
            "rows_produced_per_join": 34,
            "filtered": "100.00",
            "index_condition": "((`betaatif_store`.`cscart_discussion`.`object_id` in (597,584,573,561,556,553,549,545,541,525,521,517,513,507,497,492,489,486,482,455,453,452,451,450,449,448,447,446,445,444,443,442,394,378)) and (`betaatif_store`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "20.41",
              "eval_cost": "3.40",
              "prefix_cost": "23.81",
              "data_read_per_join": "816"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        }
      ]
    }
  }
}