Missing Data
In the real world of business or scientific reporting and analysis, data can prove to be awkward. It can be plain wrong or it can be altogether missing. Sure, we have the NULL to signify unknown, but that doesn't play well with regular business reporting. There are a number of ways of dealing with missing information, and methods of estimating data from existing data has a long and respectable history. Joe Celko gets to grips with a data topic that is often treated with some trepidation.
