Question: Find name of the services that has never been used.
Schema: create table services (service_name varchar, PRIMARY KEY (service_name)); create table party_services (service_id varchar, PRIMARY KEY (service_id)); create table services (service_name varchar, service_id varchar, PRIMARY KEY (service_name))
SQL: select service_name from services except select t1.service_name from services as t1 join party_services as t2 on t1.service_id = t2.service_id