backfill results for the same month and year

[HaidarPesebe]

Dear All,

I have the following data

ID CITY      QTY   MONTH YEAR
-------------------------------
1  Chigago    10     11       2010
1  NewYork   22     11       2010
1  London     54     11       2010
1  Chigago    7      10       2010
1  NewYork   26     10       2010
1  London     33     10       2010

ID = ID PRODUCT.

How can I backfill results with the same ID by month and year, with results like this:

MONTH/YEAR    QTY TOTAL
---------------------------
11/2010            86
10/2010            66
and etc.

Please help

Thanks
haidarpesebe