How can I sort by column headings in php mysql?

[RichGags]

I set up a results page which shows me results from my query...

$query_WADAproperties = "SELECT id, pic, address, city, state, submarket, type, class, year, buildingsize, floorsize, space, broker, annualrent FROM properties ORDER BY id ASC";

How would I set up the ORDER BY to be a variable so when I click on a column heading it passes the variable to the php and re-sorts it?

I would think that I need to declare a variable that defaults to "id" if nothing is passed to it and put it somewhere in the php.... and make the headings clickable, pointing back to the results.php with a parameter, but have no idea how.

Thanks!
Rich