//判断网址是否存在        if (Navigation.BeUrl(url))      {        sperror.InnerText = "网址你已经存在数据库了!";        return;      }查询网址是否存在数据库public static bool BeUrl(string url)    {      string sql = "SELECT count(1) FROM [navurl] WHERE [url]=@url";      SqlParameter parameters = new SqlParameter("@url", SqlDbType.VarChar,50);      parameters.Value = url;      return DbHelper.Exists(sql, parameters);      }