I'm at odds with the first two reviewers, but I think it depends on what you're looking for. This book is NOT about classical tuning. Classical tuning is "tune the server", and "tune the query".
The emphasis - in the preface and the excellent Chapter 6 - is that the real gains are usually elsewhere, when you have older code.
I work with a 25 year heritage of fairly well written apps. Many of them have the described situation - a single query that's been broken into two or more parts, with an outer loop and (at least one) inner loop. When server memories were 64K, or 1 Meg, or 4 Meg, and CPU's only came in packages of 1, and disk channels were slow, and networks were slower, this was often the only practical way to get a result.
The interplay changed over the years, but the old code worked. In the past few years, with 64-bit processors, cheap 64-CPU servers, and multi-io disk channels, a wierd thing happened. We found that moving to newer systems and faster hardware made things run SLOWER.
The answer time and again was in those "split loop queries". If we turned them back into one big query - the kind that you couldn't run before, we would see performance improvements of hundreds or thousands of times. In the end, the math proved - on powerful machines, most of the overhead is sending the query, compiling it, and sending it back. If one monster query takes a full second, but every query in the loop takes 1/4 second - if that inner loop runs 1000 times, you lose.
Meantime, that 64-core machine has every CPU working full blast - recompiling the same stupid statement over and over! The problem is, you try to tell this to a developer, they don't beleive you "I didn't change anything in the code".
And that's what this book is about. Changing the code. This book validates what I've been trying to tell my managers and coders; I am grateful to Faoult and L'Hermite for showing I was not making this up myself.
The second reviewer is just reading the wrong book for whatever it is they are trying to do.
This is an essential book for certain people, and is certainly of no interest whatsoever for others. (If you don't own a 1941 Plymouth, the 1941 Plymouth manual isn't much use - otherwise, it's a must).