how to compare two values from same textbox

[khalidhabib.cs]

function Show_charges(str,str2)
{
//alert(“Working”);
var xhr;
if(window.XMLHttpRequest){
// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}

		else {
			// code for IE6, IE5
			xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
				  }
			xmlhttp.onreadystatechange=function(){
						
		if (xmlhttp.readyState==4 && xmlhttp.status==200){
			
			document.getElementById("result").innerHTML=xmlhttp.responseText;
					}
				 }
				// alert(str2);
			xmlhttp.open("GET","reply.php?q="+str+"&q2="+str2,true);
			xmlhttp.send();
						}//End of Ajax Function show charges  from Database

This is php file
include(’…/include/db.php’);
$q= $_GET[‘q’];
$q2= $_GET[‘q2’];
?>

<?php $sql="SELECT service_amount FROM service_charges WHERE quantityFrom >='1' AND quantityTo <='4'"; and herer function calling