Sorting Multidimesional array

usort.php

function cmp($a, $b) {

                        if ($a['TotalEarnings'] == $b['TotalEarnings']) {
                            return 0;
                        }

                        if ($_GET['sortby'] == "earnings"):
                            $orderBy = ($_GET['order'] == 'a') ? "DESC" : "ASC";
                        endif;
                        if ($orderBy == "DESC"):
                            return ($a['TotalEarnings'] < $b['TotalEarnings']) ? -1 : 1;
                        else:
                            return ($a['TotalEarnings'] > $b['TotalEarnings']) ? -1 : 1;
                        endif;
                    }
                    
                    usort($mediaArray, "cmp");