Joins and Subqueries

1. Retrieve the start times of members' bookings ✓
2. Work out the start times of bookings for tennis courts ✓
3. Produce a list of all members who have recommended another member ✓
4. Produce a list of all members, along with their recommender ✓
5. Produce a list of all members who have used a tennis court ✓
6. Produce a list of costly bookings ✓
7. Produce a list of all members, along with their recommender, using no joins. ✓
8. Produce a list of costly bookings, using a subquery ✓