select mems.firstname as mem_fname, mems.surname as mem_sname, recs.firstname as rec_fname, recs.surname as rec_sname
from
members mems
left outer join
members recs
on recs.memid = mems.recommendedby
order by mem_fname, mem_sname;
select facs.name, sum(slots * case
when memid = 0 then facs.guestcost
else facs.membercost
end) as revenue
from bookings bks
inner join facilities facs
on bks.facid = facs.facid
group by facs.name
order by revenue;
select distinct mems.firstname, mems.surname, facs.name as facility_name
from
members mems
inner join bookings bks on mems.memid = bks.memid
inner join facilities facs on bks.facid = facs.facid
where
facs.name like 'Tennis Court%'
order by 1,2,3
SELECT customers.name, orders.order_date, orders.amount
FROM customers
LEFT JOIN orders
ON customers.id = orders.customer_id;