List all the patients who have an undergoing treatment.
select distinct patient from undergoes as t1 join patient as t2 on t1.patient = t2.ssn
Among them, who are staying in room 111?
select * from undergoes as t1 join patient as t2 on t1.patient = t2.ssn join stay as t3 on t1.stay = t3.stayid where t3.room = 111
What are their names?
select distinct t2.name from undergoes as t1 join patient as t2 on t1.patient = t2.ssn join stay as t3 on t1.stay = t3.stayid where t3.room = 111