Microsoft often provides free access to selected O’Reilly titles via the Microsoft Learn portal. Search the Microsoft Learn knowledge base for "Azure Data Explorer reference" — sometimes entire book chapters are embedded directly in the learning paths.
You can access the above write-up online for free from the following websites: Microsoft often provides free access to selected O’Reilly
Coursera and Udemy also offer free online courses on Azure Data Explorer. You can search for the courses on these websites. and learn on the go.
Buying the paperback is great, but accessing it digitally for free allows you to search, copy-paste queries, and learn on the go. Microsoft often provides free access to selected O’Reilly