SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    596, 593, 762, 981, 972, 708, 958, 710, 
    642, 722, 656, 793, 615, 490, 1145, 986, 
    1158, 1076, 689
  )

Query time 0.00078

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "range",
          "possible_keys": ["parent"],
          "key": "parent",
          "key_length": "3",
          "used_key_parts": ["parent_id"],
          "rows": 22,
          "filtered": 100,
          "index_condition": "cscart_categories.parent_id in (596,593,762,981,972,708,958,710,642,722,656,793,615,490,1145,986,1158,1076,689)"
        }
      }
    ]
  }
}