Table schema:
CREATE TABLE Lessons (staff_id VARCHAR); CREATE TABLE Staff (first_name VARCHAR); CREATE TABLE Staff (first_name VARCHAR, staff_id VARCHAR)

Question: What is the first name of the staff who did not give any lesson?
SQL: SELECT first_name FROM Staff EXCEPT SELECT T2.first_name FROM Lessons AS T1 JOIN Staff AS T2 ON T1.staff_id = T2.staff_id