Table schema:
CREATE TABLE CUSTOMER (LastName VARCHAR); CREATE TABLE CUSTOMER (LastName VARCHAR, CustomerId VARCHAR); CREATE TABLE Invoice (CustomerId VARCHAR, total INTEGER)

Question: Find all the customer last names that do not have invoice totals larger than 20.
SQL: SELECT LastName FROM CUSTOMER EXCEPT SELECT T1.LastName FROM CUSTOMER AS T1 JOIN Invoice AS T2 ON T1.CustomerId = T2.CustomerId WHERE T2.total > 20