SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    280, 279, 282, 276, 277, 265, 275, 264, 
    272, 271, 268, 284, 267, 281, 273, 270, 
    283, 269, 274, 266, 278
  )

Query time 0.00047

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "ALL",
      "possible_keys": ["parent"],
      "rows": 21,
      "filtered": 100,
      "attached_condition": "(cscart_categories.parent_id in (280,279,282,276,277,265,275,264,272,271,268,284,267,281,273,270,283,269,274,266,278))"
    }
  }
}