php解决表单重复提交问题

[PHP]代码  

<?php
 session_start();
 $_SESSION[&#39;num&#39;] = 0;
 if(isset($_POST[&#39;action&#39;] && $_POST[&#39;action&#39;]==&#39;submit&#39;)){
  if($_SESSION[&#39;num&#39;] == 0){
   echo &#39;<a href="&#39;.$_SERVER[&#39;PHP_SELF&#39;].&#39;">&#39;请再次尝试</a>;&#39;
   $_SESSION[&#39;num&#39;] = 1;
  }else{
   echo &#39;您已经提交过了，请不要重复提交&#39;;
  }
 } 
?>