怎么加递减的排序怎么加入？加在哪？

就是这段代码，我加了出错！我要加个递减 的排序 DESC 加哪？按开通时间递减，就更好了！帮帮忙
$star = array();
$starlist = array();
if($_SCONFIG['spacebarusername']) {
        $query = $_SGLOBAL['db']->query("SELECT * FROM ".tname('space')." DESC WHERE username IN (".simplode(explode(',', $_SCONFIG['spacebarusername'])).")");
        while ($value = $_SGLOBAL['db']->fetch_array($query)) {
                realname_set($value['uid'], $value['username'], $value['name'], $value['namestatus']);
                $starlist[] = $value;
        }
}
if($starlist) {
        $star = sarray_rand($starlist, 1);
}

有人晓得吗？