In my training and consulting experience on Power BI, I realized that DAX is the weak point for many Power BI users. DAX itself is not a complex language. It is merely a language of expression. The complexity of learning DAX is not the formula or the functions. It is how to use it in real-world scenarios and how it performs on a dataset or visual.
I have been writing many blogs about DAX for many years. My blog articles are all coming from my experience working with Power BI. I found it helpful to compile them all in a book. Because my blog articles practically explain things, I thought it better to title it as a practical way of learning DAX by examples.
Indeed, there are books, articles, and Microsoft documentation on how each function works where and how. However, learning these through an example would bring a new way of understanding it.
A good analytics solution is a combined outcome of a good data model, good data preparation, and good analytics and calculations. I have written another book about the Basics of modeling in Power BI. This book is covering the calculation and DAX aspects of it.