What are the names of all employees who have a certificate to fly 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"
employees who have a certificate to fly Boeing 737-800 refers to a JOIN between Employee, Certificate, and Aircraft tables with a condition on Aircraft.name = 'Boeing 737-800';