Learn for Free KQL–the language Log Analytics and other services use

KQL, the Kusto Query Language, is used to query Azure's services. This course will teach you the basic syntax of KQL, then cover advanced topics such as machine learning and time series analysis, as well as exporting your data to various platforms.

https://www.pluralsight.com/courses/kusto-query-language-kql-from-scratch

I've been using KQL for quite a while, but still found this course useful, there were some operators I’d never used and I think I have a better understanding of JOINS and UNIONS now. 

I particularly like the pace of the delivery, the practical examples and also the way Robert lays out the syntax in a very readable way. You can also download the code samples (open the .CSL files in Notepad) and slides for your reference.