Sales Report

Hi I'm trying to write a query that will produce a sales volume report for the last month for an e-commerce store. Its based around an Access Database. Table Structure follows.

Products
productid PK
name

Orders
orderID PK
date

Orderitems
id PK
orderid FK
productid FK
quantity

I have this

Code:
SELECT products.productid, Sum(orderitems.quantity) AS totalsold, products.[name] FROM orderitems, products, orders
WHERE products.productid= orderitems.productid  AND orders.orderid=orderitems.orderid AND orders.[date]> DateAdd ("m", -1, date())
GROUP BY products.[name], products.productid
Which gives me the number of each item sold in the past month, but only for items where there have actually been sales. How would I adjust this to give me sales figures of 0 for products which haven't sold?

I'm guessing its something like this:

Code:
SELECT products.productid, products.[name], IIF(Sum(orderitems.quantity)  IS NULL, 0, Sum(orderitems.quantity)) AS totalsold
FROM products LEFT OUTER JOIN  orderitems ON orderitems.productid = products.productid INNER JOIN orders ON orders.orderid=orderitems.orderid
WHERE  orders.[date]> DateAdd ("m", -1, date())
GROUP BY products.[name], products.productid
But I can't seem to get my nested joins right and the Access brackets around them.

Can anyone help?

Thanks