CREATE TABLE aircraft (aid DECIMAL, name TEXT, distance DECIMAL)
CREATE TABLE employee (eid DECIMAL, name TEXT, salary DECIMAL)
CREATE TABLE flight (flno DECIMAL, origin TEXT, destination TEXT, distance DECIMAL, departure_date TIME, arrival_date TIME, price DECIMAL, aid DECIMAL)
CREATE TABLE certificate (eid DECIMAL, aid DECIMAL)

What are the ids of all employees that don't have certificates?
SELECT eid FROM employee EXCEPT SELECT eid FROM certificate
SELECT "eid" FROM "employee" EXCEPT SELECT "eid" FROM "certificate"