here is my solution
IMO, a few things were ambiguous.
1. 1st instruction is to combine the two lists and ensure no duplicate USERS. Well, the first two lists don;t have USERs, but there is one duplicate store...
2. 2nd instruction is to combine user details (there are no duplicate users). but there is user information for non-existent stores, and there are stores that have no user. The final solution drops stores for both cases, but the instructions could be clearer (ie, as would be the case if working on a real-world problem, and would need to decide how to handle each situation).
Not a big deal on a practice exercise, but would be problematic if this were an exercise on the core certification exam!
Curious if anyone else felt there is some ambiguity?