Get opposite result of INNER JOIN

There is Table A and B

item_serial_no (Table A)  | forbidden_item_serial_no (Table B)
--------------            | --------------
1                         | 1
2                         | 3
3                         | 5
4                         | 7
5
6
7

When I use SQL:

SELECT
A.item_serial_no
FROM
A
INNER JOIN B ON A.item_serial_no = B.forbidden_item_serial_no

I will get 1,3,5,7.

But I would like to get negation of it, so the result would be like:

result query
------------
2
4
6

I am not SQL ninja and I have spent prety much time to solve this, but no success.
Thanx for help

>Solution :

One way of doing this is to use a LEFT JOIN:

SELECT
A.item_serial_no
FROM
A
LEFT JOIN B ON A.item_serial_no = B.forbidden_item_serial_no
WHERE B.forbidden_item_serial_no IS NULL