Produce a list of costly bookings, using a subquery

Question

How can you produce a list of bookings on the day of 2012-09-14 which will cost the member (or guest) more than $30? Remember that guests have different costs to members (the listed costs are per half-hour 'slot'), and the guest user is always ID 0. Include in your output the name of the facility, the name of the member formatted as a single column, and the cost. Order by descending cost.

Answers and Discussion Show

select member, facility, cost from (
	select 
		mems.firstname || ' ' || mems.surname as member,
		facs.name as facility,
		case
			when mems.memid = 0 then
				bks.slots*facs.guestcost
			else
				bks.slots*facs.membercost
		end as cost
		from
			cd.members mems
			inner join cd.bookings bks
				on mems.memid = bks.memid
			inner join cd.facilities facs
				on bks.facid = facs.facid
		where
			bks.starttime >= '2012-09-14' and
			bks.starttime < '2012-09-15'
	) as bookings
	where cost > 30
order by cost desc;