PHP & SQL - Sum some value from db

PHP & SQL - Sum some value from db

I have table like this
A
======
2
7
7
8
9
3
...
1
======
I need to sum all value of row in db, except last value (that is '1'). I
know how to sum all value, my question how to sum all value except last
value?
$sum = 0;
$a = mysql_query('SELECT A FROM tbl');
while($row = mysql_fetch_array($a))
{
$jpos = $row['A'];
$sum += intval($jpos);
}
echo $sum;
thanks for your response.