SQL question

We have the following SQL query, that works very well:

select year,
month,
sum(sales) as sales
from foo
where (year * 100 + month) > ((year(current_date) -1) * 100 +
month(current_date))
group by year, month
order by year, month

But now, we want to add a fourth column, for the previous year's sales. Now, I can get this by itself (I think) with something like this:

select year+1 as year,
month,
sum(sales) as py_sales
from foo
where ((year * 100 + month) > ((year(current_date) -2) * 100 + month(current_date)))
and ((year * 100 + month) <= ((year(current_date) -1) * 100 + month(current_date)))
group by year, month
order by year, month

But how would I combine these to get both the "sales" and "py_sales" columns? Some kind of a join, maybe? But what would the syntax be?

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JHHL