SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    8164, 8161, 8163, 9766, 8750, 9765, 8162, 
    8670, 8735, 8733, 8158, 8157, 8160, 
    8166, 8751, 8741, 8159, 9767, 8668, 
    8763, 8731, 8734, 8165, 8732
  )

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.16"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 24,
      "rows_produced_per_join": 24,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "2.76",
        "eval_cost": "2.40",
        "prefix_cost": "5.16",
        "data_read_per_join": "62K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (8164,8161,8163,9766,8750,9765,8162,8670,8735,8733,8158,8157,8160,8166,8751,8741,8159,9767,8668,8763,8731,8734,8165,8732))"
    }
  }
}

Result