using LIMIT only on primary table

If I want the last 100 orders:

SELECT * FROM orders LIMIT 100;

If I want all the items on the last 100 orders, I'd start like this:

SELECT * 
from orders, order_items 
where order_items.order_id = orders.id
LIMIT 100

But that will only give me the last 100 items, not 100 orders.

What I really want is 

SELECT * 
from orders, order_items 
where order_items.order_id = orders.id
and exists
(SELECT * from orders order by ID DESC limit 100);

But that gives me all orders, not just the first 100.

Adding a LIMIT 100 to the above doesn't work either.  It equates to the 
first example.

Clues?  cheers
-- 
Dan Langille
The FreeBSD Diary - http://freebsddiary.org/ - practical examples