Hey what a coincidence! I dunno why he failed with the 4th one.<p>We maintain a leasing administration system here, and one of the most important/critical features is doing the thing he describes. You can know the exact state of any leasing contract (or a group, or all of them) by chosing a date of the future and past. That way you can compare the expected result vs reality. It is implemented fully inside a SQL DBMS (and works fine)....