Smarty未定义的索引变量

Question

I am newbie to smarty and trying to output some results in my tpl file fetching from php. In my account.php file I have put Below code

<?php
  include SMARTYLOADER;
  $ad2 = $db->fetchRow("SELECT * FROM ip_ptc");
  $smarty->assign("ad2", $ad2);
  $smarty->display("account.tpl");
  $db->close();
  exit();
 ?>

and in my account.tpl file i have written below code to fetch the result

{$ad2.country}

but it is showing an undefined index variable ad2 what's wrong i am doing