Find rows for a value with different dates in the same table

Need a single query/subquery

[dougmcc1]

Assuming the fields in a single table are Date¦Product¦Sales, I want to return all products that had fewer sales yesterday than the day before.

What would be the query for this?

Thanks in advance.

[dougmcc1]

Also, how do I return the difference in sales, ordered by difference in sales descending?