The data and relationships in any database are only ever a subset of the real world with just the attributes and relationships that matter to how your database needs to work. As well as explaining all the concepts you need to build and design databases, Celko shows why these matter and how to decide what entities to use to represent data. He covers the major database design techniques; this soon becomes technical, with code snippets and references to various database theories, but usually the examples make sense of it all.
The section on time is fascinating as well as useful, but while the Y2K discussion covers all the important issues, it does seem dated, referring to problems in DOS and Windows 3.1 rather than Windows NT or Windows 95/98. Read this to understand the problem, not for information on how to fix it. The details of how to deal with numerical data, text and "exotic" data like multimedia and geographical information, how to encode data, and how to check for errors are certainly useful, but oddly all of these come before the explanation of what relational databases actually are and how they work.
You'll still need to learn the specifics of whatever database application you plan to use, but if you're a computer professional and you need a fast introduction to the nuts and bolts of database theory and programming, start here. --Penny Jannifer, amazon.co.uk