Division on columns giving error

$c = $modx->newQuery('starRating');
$c->select('vote_total/vote_count AS rating, star_id');
$c->sortby('rating','ASC');
$c->prepare();
echo ($c->toSql());

$ratings = $modx->getCollection('starRating', $c);
foreach ($ratings as $rating) {
   $output.= $rating->get('star_id').',';
}

 SELECT vote_total/vote_count AS rating, `star_id` FROM `modx_star_rating` AS `starRating` ORDER BY rating ASC