It’s not you; I have a hunch it’s the data model, 
specifically the lack of a transaction register. Imagine a [flat] list of every course purchased, the course ID, the member, and the date.
- Filter for customer
- Sort on date (ascending)
- Bob’s your uncle.
What am I missing?
Correct, and it probably never should have been stored in separate tables. Sure, you want to render it that way for particular requirements, but typically, the most basic data structure is the one that will afford the greatest agility, and that’s the good’ol trusty transaction register (i.e. transactional data).
