I started in a new Operations role in a software company that used DB2 as their target database. I had previoulsy used MySQL on other applications but after a short while trying to figure out DB2 I knew that it would take more than online manuals to get a good understanding of the architecture of DB2. I didn't find many books on DB2 (as opposed to the hundred or so for Oracle) but fortunately 'Understanding DB2' is one of the best technical books I've bought.
The first couple of chapters take you through the basics of DB2 such as it's admin and monitoring tools, DB2 environment and even and introduction into database partitioning. The language used is very clear without being overly wordy and the diagrams provide good aids to understanding the structure of DB2.
I was a bit cautious about the 'Learning Visually with Examples' subtitle of the book as I didn't want almost a thousand pages of useless Windows screen shots with little explanation. However the authors have done a good job to ensure all diagrams and screenshots are appropriate. In fact there a less GUI screenshots than you might expect because a lot of DB2 is operated from the command line. It is good that most time was spent with the command line because a GUI are not always available (I work with DB2 on Unix and Windows) and while it's easy to understand the GUI after knowing the command line, the reverse is not true.
I especially liked the practical nature of the book, including the case studies at the end of each chapter which take you through possible real life examples of what you've just learnt. The questions also help to make sure you've understood the chapters.
It should be noted that this is not a book to teach you SQL. While it has a chapter on SQL, this gives you an introduction to many of the commonly used commands. SQL is a big language and is best dealt in a book of it's own. But if you haven't used much SQL before, this book will give you enough to get by so I would rush out to buy a companion just yet.
To be honest, I can't really find a fault with this book. I've read about 2 thirds of it line by line and have used it when necessary to get me out of problems at work. I would recommend this book to beginners and intermediate DBAs. There are a number of references available from the IBM website, but only after gaining a good grounding of the nature of DB2 to these really make sense. And that is exactly what this book provides.