Show me the monthly rentals for all student addresses.
select address_id, monthly_rental from student_addresses
Give me the id of address with highest monthly rental.
select address_id from student_addresses order by monthly_rental desc limit 1
What about its zip code?
select t2.address_id, t1.zip_postcode from addresses as t1 join student_addresses as t2 on t1.address_id = t2.address_id order by monthly_rental desc limit 1