I've been doing analysis / data science for a few years now. Lately i've been considering a jump to data engineering. It's intimidating how much there is to learn, but this looks like an excellent resource for deeply understanding sql. Thanks!

Just read the first chapter. This is gold, but how is the author making money off it?

I'm selling it as book.

But more importantly: the "fame" sells other services. Look here: https://winand.at/

Is it possible that the online book is stealing some posible revenue that would come from support?

It is absolutely possible.

On the other hand: it's also possible that nobody would know me without the website.

Further: I've learned so much from free online resources, why not giving something back?

I know for sure that many people buy the book because they started reading online. Also: A lot of the training I do is sold because ONE participant has read the site/book and arranges a training for the department.

TL;DR: I works fine for me.

SQL performance is exactly the issue I'm having with my current project, so this popped up at the perfect time. Going to have to read it cover-to-cover I think.

Thanks!