SQL question

["James H. H. Lampert" <jamesl@xxxxxxxxxxxxxxxxx>]

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?

--
JHHL