Show names for all employees.
select name from employee
Also show the name of aircraft on which they have a certificate.
select t1.name, t3.name from employee as t1 join certificate as t2 on t1.eid = t2.eid join aircraft as t3 on t3.aid = t2.aid
Which of those employees have certificate of Boeing 737-800?
select t1.name from employee as t1 join certificate as t2 on t1.eid = t2.eid join aircraft as t3 on t3.aid = t2.aid where t3.name = "Boeing 737-800"