Window functions are probably the most confusing part of SQL. You might think, "So what? They just added a few extra functions". Not really. "Window functions" is a separate language built into regular SQL. And it's more complicated than anything you know about SELECTs.
I've read several dozen articles explaining SQL window functions. They all suffered from one of two problems: (1) Easy read without much practical value, describing 10% of features, or (2) Difficult to comprehend (if I did not know the subject — I would not understand a thing).
I wanted people to understand SQL windows better. So I wrote a book on window functions with a hundred pictures and GIFs explaining everything, and fifty-six interactive exercises to turn abstract knowledge into skills.
Here it is.
