Datalog not "click" to me. Is weird to understand and another uncommon programming model, and think that the ideao of build a relational language exhaust the limit of paradigm switch for my potential users. However I wonder if can be used as a internal engine and will provide efficient/easier backend for all the relational stuff?
It's almost 'free' if you know even just basic Prolog.
I learnt it before Prolog, and personally really like it, much more than I do SQL. It's a slightly different mindset - "what is a result" rather than "how do I go about finding a result" - but one that I found more intuitive in an Intro to DB course.