SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    305, 302, 271, 284, 315, 298, 311, 291, 
    285, 277, 266, 322, 317, 281, 308, 306, 
    303, 286, 292, 272, 312, 267, 323, 299, 
    316, 318, 278, 309, 282, 307, 304, 287, 
    293, 273, 283, 300, 279, 310, 313, 319, 
    268, 324, 294, 288, 314, 320, 274, 301, 
    325, 280, 269, 295, 289, 326, 270, 275, 
    321, 290, 296, 276, 327, 297
  )

Query time 0.00218

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.25"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "index",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 60,
      "rows_produced_per_join": 60,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "0.25",
        "eval_cost": "6.00",
        "prefix_cost": "6.25",
        "data_read_per_join": "156K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`aerokidsshop`.`cscart_categories`.`parent_id` in (305,302,271,284,315,298,311,291,285,277,266,322,317,281,308,306,303,286,292,272,312,267,323,299,316,318,278,309,282,307,304,287,293,273,283,300,279,310,313,319,268,324,294,288,314,320,274,301,325,280,269,295,289,326,270,275,321,290,296,276,327,297))"
    }
  }
}