CREATE TABLE Aircraft (aid VARCHAR, name VARCHAR)
CREATE TABLE Certificate (eid VARCHAR, aid VARCHAR)
CREATE TABLE Employee (name VARCHAR, eid VARCHAR)

Show names for all employees who have certificates on both Boeing 737-800 and Airbus A340-300.
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" INTERSECT 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 = "Airbus A340-300"
SELECT "T1"."name" FROM "Employee" AS "T1" JOIN "Certificate" AS "T2" ON "T1"."eid" = "T2"."eid" JOIN "Aircraft" AS "T3" ON "Boeing 737-800" = "T3"."name" AND "T2"."aid" = "T3"."aid" INTERSECT SELECT "T1"."name" FROM "Employee" AS "T1" JOIN "Certificate" AS "T2" ON "T1"."eid" = "T2"."eid" JOIN "Aircraft" AS "T3" ON "Airbus A340-300" = "T3"."name" AND "T2"."aid" = "T3"."aid"