Section 1.4. Qualifying Boolean Columns

1.4. Qualifying Boolean Columns

Even though the Boolean type doesn't exist in SQL, many people feel a need to implement flags to indicate a Boolean true/false status (for instance order_completed). You should aim for increasing the density of your data--order_completed may be useful information to know, but then perhaps other information would be nice to store too: when was it completed? Who completed it? So that means that instead of having a single "Y/N" column, we can have a completion_date column, and perhaps a completed_by column, both of which will tell us more (although we may not necessarily want to see a null value as long as the order isn't completed; a solution may be to use a distinct table to track the various stages of every order from creation to completion). As before, examine the dependencies in the context of your business requirements, and only include those additional columns where the successful operation of the business requires it.

Alternatively, a series of essentially Boolean attributes can sometimes be advantageously combined into a unique status attribute. For instance, if you have four attributes that can be either true or false, you can assign a numerical value between 0 and 15 to each of the possible combinations and define the "status" as being represented by this value. But bewarethis technique may offend the basic rule of atomicity, so if you must use this approach, do so with considerable caution.

Data for data's sake is a path to disaster.