SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    295, 598, 599, 301, 300, 586, 299, 587, 
    560, 558, 562, 296, 298, 297, 380, 390, 
    559
  )

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "11.91"
    },
    "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": 17,
      "rows_produced_per_join": 17,
      "filtered": "100.00",
      "index_condition": "(`zdrowy_db`.`cscart_categories`.`parent_id` in (295,598,599,301,300,586,299,587,560,558,562,296,298,297,380,390,559))",
      "cost_info": {
        "read_cost": "10.21",
        "eval_cost": "1.70",
        "prefix_cost": "11.91",
        "data_read_per_join": "109K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ]
    }
  }
}