<?php
 //session_start();
 //$_SESSION['a']="10";
?>
<html>
<head>
	<title></title>
</head>
<body>
<form action=test2.php?b=20& method=get>
  <input type=text name='a'>
  <input type=submit> 
</form>
  <a href="test2.php?a=20">clcik here</a>
</body>
</html>