What are the last names of customers without invoice totals exceeding 20?
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
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
[{'LastName': 'Almeida'}, {'LastName': 'Barnett'}, {'LastName': 'Bernard'}, {'LastName': 'Brooks'}, {'LastName': 'Brown'}, {'LastName': 'Chase'}, {'LastName': 'Dubois'}, {'LastName': 'Fernandes'}, {'LastName': 'Francis'}, {'LastName': 'Girard'}, {'LastName': 'Gonçalves'}, {'LastName': 'Gordon'}, {'LastName': 'Goyer'}, {'LastName': 'Gray'}, {'LastName': 'Gruber'}, {'LastName': 'Gutiérrez'}, {'LastName': 'Hansen'}, {'LastName': 'Harris'}, {'LastName': 'Hughes'}, {'LastName': 'Hämäläinen'}, {'LastName': 'Johansson'}, {'LastName': 'Jones'}, {'LastName': 'Köhler'}, {'LastName': 'Leacock'}, {'LastName': 'Lefebvre'}, {'LastName': 'Mancini'}, {'LastName': 'Martins'}, {'LastName': 'Mercier'}, {'LastName': 'Miller'}, {'LastName': 'Mitchell'}, {'LastName': 'Murray'}, {'LastName': 'Muñoz'}, {'LastName': 'Nielsen'}, {'LastName': 'Pareek'}, {'LastName': 'Peeters'}, {'LastName': 'Peterson'}, {'LastName': 'Philips'}, {'LastName': 'Ralston'}, {'LastName': 'Ramos'}, {'LastName': 'Rocha'}, {'LastName': 'Rojas'}, {'LastName': 'Sampaio'}, {'LastName': 'Schneider'}, {'LastName': 'Schröder'}, {'LastName': 'Silk'}, {'LastName': 'Smith'}, {'LastName': 'Srivastava'}, {'LastName': 'Stevens'}, {'LastName': 'Sullivan'}, {'LastName': 'Taylor'}, {'LastName': 'Tremblay'}, {'LastName': 'Van der Berg'}, {'LastName': 'Wichterlová'}, {'LastName': 'Wójcik'}, {'LastName': 'Zimmermann'}]