Forum Discussion
Good Source to Learn DAX
There are lots of sources
Start here with guided learning
https://powerbi.microsoft.com/en-us/learning/
MS have started a new learning site. Its new so there isn't much yet, but they are adding more.
https://docs.microsoft.com/en-us/learn/browse/?products=bizapps-power-bi
There is a free edx course
https://courses.edx.org/courses/course-v1:Microsoft+DAT207x+1T2017/course/
Curbal is a fantastic chanel ruthpozuelo has loads of videos on lots of Dax functions.
https://www.youtube.com/channel/UCJ7UhloHSA4wAqPzyi6TOkw
Powerbi tips have a good set of links to sites including learning
Post PatronThis resource is proving to be very well written!
https://bengribaudo.com/blog/2018/01/19/4321/power-query-m-primer-part4-variables-identifiers
Helper II'd like to add the following great (free) DAX course from EnterpriseDNA (not affiliated)
http://portal.enterprisedna.co/p/ultimate-beginners-guide-to-dax
DAX fridays with Ruth from Curbal.com is also a great learning source.
https://www.youtube.com/channel/UCJ7UhloHSA4wAqPzyi6TOkw
DAX Patterns is a list of common patterns to solve common problems.
When it comes to books I would like to recommend "Supercharge Power BI: Power BI Is Better When You Learn to Write DAX" by Matt Allington. It contains a lot of exercises that will help you solidify your learning. It is a great introduction to DAX.
https://www.amazon.com/Supercharge-Power-BI-Better-Learn/dp/1615470522?tag=exccbs-20
The Definitive Guide to DAX is the DAX bible. Apparently a new edition is coming out in February 2019.