Column Sort Question

Hi All, This is a newbie question. I am using PHP Version 4.2.3 with register_globals=off. I am trying to creating a simple address book with mysql as the backend. I have a form that passes what the user wants to query from the address book and it returns everything in a table with column heading just fine. I use $myvar1=$_POST['myvar1']; to pass the info from the form to the php file. I am using the following in the header fields of the table: <th nowrap> <a href="<?php echo "$PHP_SELF?order_by=FIRSTNAME"; ?>">First Name</a> </th> This doesn't work (I get a bunch of errors) and I think it's because the variable from $_POST are not staying persistent. I tried playing around with session with no luck. What is the best way to resort on a column? Thanks, Jerry