The book appears to me to be the contents of use-the-index-luke.com. My friends impulsed bought it when I told him I was planning on buying it after confirming that it had more content than the website but after skimming the table of contents it doesn't appear to have anything more than the website.

Still, its good to support Markus' effort and if you prefer having a PDF rather than going to the website, just buy it. It's like $15.

Quoting from http://Use-The-Index-Luke.com/ (the main page):

Use The Index, Luke is the free web-edition of SQL Performance Explained. If you like this site, consider getting the book. Also have a look at the shop for other cool stuff that supports this site.

http://use-the-index-luke.com/shop

I was in his Modern SQL talk at FOSDEM on Saturday, he clearly knows his stuff. His book is definitely on my list.

X-comment so you get it too:

Quoting from http://Use-The-Index-Luke.com/ (the main page):

Use The Index, Luke is the free web-edition of SQL Performance Explained. If you like this site, consider getting the book. Also have a look at the shop for other cool stuff that supports this site.

http://use-the-index-luke.com/shop