Slightly different style
$q_data = sprintf('select itmid, minSell, maxSell FROM table');
$r_data = $db->query($q_data);
while(list($id,$min,$max) = mysql_fetch_array($r_data))
{
$rand_price = mt_rand($min,$max);
$q_update=sprintf('update table set sellPrice = %d where itmid = %d',$rand_price,$id);
$db->query($q_update);
}