When May You Bend or Break the Rules?
There are only two specific circumstances under which it is at all permissible to bend or break the rules of proper database design. Unless either of these is an inescapable imperative, you should use proper database-design techniques when designing your database.
Designing an Analytical Database
As you learned in Chapter 1, an analytical database stores and tracks historical and time-dependent data. This type of database often contains calculated fields within some of its table structures. The expressions used in many of these fields are meant to record the state of a particular set of data at a given moment in time; other fields store the results of aggregate functions.
You may have already surmised ...