SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 
    55, 56, 57, 58, 59
  )

Query time 0.00073

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["parent"],
      "key": "parent",
      "key_length": "3",
      "used_key_parts": ["parent_id"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_categories.parent_id in (44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59)"
    }
  }
}