SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    56, 43, 47, 42, 48, 651, 648, 665, 624, 
    595, 594, 580, 566, 554, 511, 493, 481, 
    461, 492, 421, 411, 396, 412, 358, 345, 
    344, 343, 342, 307, 280, 279, 264, 263, 
    236, 262, 239, 203, 223, 201, 204, 193, 
    172, 163, 104, 105, 153, 109, 139, 86, 
    205, 207, 85, 206, 78, 72
  )

Query time 0.00055

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "58.76"
    },
    "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": 100,
      "rows_produced_per_join": 100,
      "filtered": "100.00",
      "index_condition": "(`dbggbern`.`cscart_categories`.`parent_id` in (56,43,47,42,48,651,648,665,624,595,594,580,566,554,511,493,481,461,492,421,411,396,412,358,345,344,343,342,307,280,279,264,263,236,262,239,203,223,201,204,193,172,163,104,105,153,109,139,86,205,207,85,206,78,72))",
      "cost_info": {
        "read_cost": "48.76",
        "eval_cost": "10.00",
        "prefix_cost": "58.76",
        "data_read_per_join": "400K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ]
    }
  }
}

Result

category_id parent_id
72 56
78 56
85 56
86 56
104 56
105 56
109 56
139 56
153 56
163 56
172 56
204 56
193 56
201 56
205 56
203 56
206 56
207 56
421 56
223 56
263 56
236 56
239 56
262 56
264 56
279 56
280 56
307 56
342 56
343 56
344 56
345 56
358 56
411 56
412 56
396 56
461 56
481 56
492 56
493 56
511 56
554 56
566 56
580 56
594 56
595 56
624 56
648 56
651 56
665 56