'where and or' help needed

[APuppyDog]

i have a piece of code which subtracts credits every time a button is clicked. the original code works fine. I have since added a bonus_credit column, where i want it to function like this. if buy_credit = 0 and bonus_credit>0 then subtract from the bonus credit, but still do everything else its supposed to do..

 

here is the original code i had

	$selRes=mysql_query("SELECT buy_credit from user where id='".$hb_id."' and buy_credit>0");
if(mysql_affected_rows()>0)
{
	$b_comm=0;
	$bc_updqry=mysql_query("UPDATE user set buy_credit=buy_credit-1 where id='".$hb_id."'");
	$updqry=mysql_query("UPDATE cars set b_fee_paid_status='1' where id='".$aid."'");
}

 

here is my modified code, but it doesn't seem to subtract from buy_credit if buy_credit is >0.. it should only kick in the bonus_credit usage if buy_credit is 0

	$selRes=mysql_query("SELECT buy_credit,bonus_credit from user where id='".$hb_id."' and buy_credit>0 OR bonus_credit>0");
if(mysql_affected_rows()>0)
{
	$b_comm=0;
		if($selRes['buy_credit']!=0)
		{
		$bc_updqry=mysql_query("UPDATE user set buy_credit=buy_credit-1 where id='".$hb_id."'");
		}
		else {
			$bc_updqry=mysql_query("UPDATE user set bonus_credit=bonus_credit-1 where id='".$hb_id."'");
			}
	$updqry=mysql_query("UPDATE cars set b_fee_paid_status='1' where id='".$aid."'");
}

 

your help is appreciated.