If I correctly understood, this is not possible (two queries instead of one).
I ended up with this sad and time-consuming loop… :/
//get subtracks
$querystr = $wpdb->prepare("SELECT subtrack_id FROM `$subtracks_table` WHERE tracklist_id='%d' ORDER BY `subtrack_time` ASC",$this->post_id);
if ( !$ids = $wpdb->get_col($querystr) ) return;
//update order
$i = 0;
foreach($ids as $id){
$i++;
$wpdb->update(
$subtracks_table, //table
array('subtrack_order'=>$i), //data
array('subtrack_id'=>$id) //where
);
}