C#生成流水号

 public string GetSerialNumber(string serialNumber)
        {
            if (serialNumber != "0")
            {
                string headDate = serialNumber.Substring(0, 8);
                int lastNumber = int.Parse(serialNumber.Substring(8));
                //如果数据库最大值流水号中日期和生成日期在同一天，则顺序号加1
                if (headDate == DateTime.Now.ToString("yyyyMMdd"))
                {
                    lastNumber++;
                    return headDate + lastNumber.ToString("00");
                }
            }
            return DateTime.Now.ToString("yyyyMMdd") + "01";
        }