เรื่อง multiple อะคับ ผมทำเมนู ทั้งหมดอะคับ จะทำยังไงพอกดปุ่มทั้งหมดเเล้วไห้มันคมทั้งหมดอะคับ

<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script>
$(document).ready(function() {

  $('#lmName3').click(function(){
	var str = '';
	if($('#lmName3').val()==''){		
		$('#lmName3 option').each(function(){
			if(str==''){
				str = $(this).val();
			}else{
				str = str +','+$(this).val();
			}
		});
	}else{
		str = $(this).val();
	}

	$('#selected_list').html(str);
  });

});
</script>
<form action="" method="post" name="form1">
List Menu 3<br>
<select name="lmName3[]" size="5" multiple id="lmName3">
<option value="">ทั้งหมด</option>
<option value="x">x</option>
<option value="y">y</option>
<option value="z">z</option>
</select>
<div id="selected_list"></div><br>
<input name="btnSubmit" type="submit" id="btnSubmit" value="Submit">
</form>

<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script>
$(document).ready(function() {
  $('#lmName3').click(function(){
	if($('#lmName3').val()==''){		
		$('#lmName3 option').each(function(){
			if($(this).val() != ''){
				$(this).attr('selected','selected');
			}else{
				$(this).removeAttr('selected');
			}
		});
	}
  });

});
</script>
<form action="" method="post" name="form1">
List Menu 3<br>
<select name="lmName3[]" size="5" multiple id="lmName3">
<option value="">ทั้งหมด</option>
<option value="x">x</option>
<option value="y">y</option>
<option value="z">z</option>
</select><br />
<input name="btnSubmit" type="submit" id="btnSubmit" value="Submit">
</form>
<?php
if(!empty($_POST['lmName3'])){

	foreach($_POST['lmName3'] as $p){
	echo $p.'<br />';
	}
}
?>