SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (1, 3)

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "p_category_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "category_id"
      ],
      "key_length": "3",
      "rows": 2,
      "filtered": 100,
      "index_condition": "(`_testcscart`.`cscart_categories`.`category_id` in (1,3))"
    }
  }
}