This book is approximately 800 pages of meat. This is one of O'Reilly's "Documentation from the Source," generally meaning it is a document from the web that they have published in book form. If you want the current document, it is always available from www.mysql.com. I like having printed documentation, but I'm glad I didn't have to print this many pages myself.
This is a live, work in progress, that has been frozen in time for the book publishing process. That means that the information in the book is not without its issues. For example, I have found a URL that no longer exists, but I suspect it will have been updated on the web version. There are several references to sections that will be updated in the future. As long as you understand that you may have to go to the website for certain specific information, if it concerns you, you should be able to make use of this voluminous work. And there is a lot of information.
Except for the very large size, this document is written similarly to how I would write my own documentation. It is written at a somewhat higher level, mainly because the intended audience is expected to understand something about relational databases and SQL (Structured Query Language). It is a reference, after all, and not a tutorial. And as with my own documentation, sometimes there is lots of extra information, and other times there is minimal. It is obvious that this was written by several people. The flow and rhythm changes all the time.
There are two issues that I have with this document. The first I can live with, but is a bit disconcerting: Words such as "localizing" are spelled "localising" (note the "s" and "z"). Pick any similarly spelled word, and it's the same. For most words, I definitely prefer the often more efficient American versions.
The other issue is with this document in its book form. Although the colophon at the back of the book indicates that there were editors involved in the publication, it doesn't look like there was any English language editing being done. For example, there are some misspellings and even whole words that are incorrect (i.e. "where" instead of "were"). Although this may be forgiven in a live website document, these sorts of errors should never make it to a printed book.
Overall, though, there is lots of very pertinent information. I only read through the sections that I thought were relevant for me, and glossed over such things as the C API. I'll be glad to have this reference handy when I start doing some MySQL creations.