Databse ER Design for Apartment Complex and Automaker Employees
I think overall you have a decent enough design there. My only points of issue might be with the Invoice Table having a calculated field (TotalNights) and that the Discount uses just the DiscountID, not the amount being discounted. Like this, a person looking at the table would have to JOIN to the Discount Table to see what the discount is by itself, unless he wanted to do the manual math of breaking down the Total, Flat Rate and Discount amount.