CREATE TABLE Customers (Address_ID VARCHAR2)
CREATE TABLE Addresses (City_Town VARCHAR2, Address_ID VARCHAR2)
CREATE TABLE Performers (Address_ID VARCHAR2)

Show all cities where at least one customer lives in but no performer lives in.
SELECT T1.City_Town FROM Addresses AS T1 JOIN Customers AS T2 ON T1.Address_ID = T2.Address_ID EXCEPT SELECT T1.City_Town FROM Addresses AS T1 JOIN Performers AS T2 ON T1.Address_ID = T2.Address_ID
SELECT "T1"."City_Town" FROM "Addresses" "T1" JOIN "Customers" "T2" ON "T1"."Address_ID" = "T2"."Address_ID" EXCEPT SELECT "T1"."City_Town" FROM "Addresses" "T1" JOIN "Performers" "T2" ON "T1"."Address_ID" = "T2"."Address_ID"