For changing the default data store a third option is filter statements that filter only the default data source, without filtering the original result set. This is useful with statements containing two or more subqueries that contain the same filter. For this I used a WITH ... FOR () construction.
It was actually quite hard to come up with a good and simple example, but here is a go:
"show all apple sales for departments that sold apples in January and the pear sales for departments that did not sell apples in January"