what is the maximum cost of a hospital that involves a drug named acetaminophen w/codeine until 2 years ago?
select max(t1.c1) from ( select sum(cost.cost) as c1 from cost where cost.hadm_id in ( select prescriptions.hadm_id from prescriptions where prescriptions.drug = 'acetaminophen w/codeine' ) and datetime(cost.chargetime) <= datetime(current_time,'-2 year') group by cost.hadm_id ) as t1