month
------------
month_id -- 1-12
month_name -- Jan - Dec

Sales
------------
month_id  --not every month has sale
product
amount

select
    month_name
    ,product
    ,sum(isnull(amount,0))
from
    month
    left outer join sales
        on sales.month_id = month.month_id
group by
    month_name
    ,product