function get_class($i){
 
   if($i==1)
   class_url = 'product_class.php';
   else if($i==2)
   class_url = 'admin/product/front/product_class.php';
   else
   class_url = '../../product/front/product_class.php';
 
   $.ajax({
      url: class_url,         
	  cache: false,         
	  dataType: 'html',             
	  type:'POST',         
	  data: {i:$i},
	  error: function(xhr) { alert('Ajax request 發生錯誤'); }, 
	  success: function(response){ $('#left').html(response);    }	 
	  }); 
   
 }