Question: Which first names are used for professionals or owners but are not used as dog names?
Schema: create table owners (first_name varchar, name varchar, PRIMARY KEY (first_name)); create table dogs (first_name varchar, name varchar, PRIMARY KEY (first_name)); create table professionals (first_name varchar, name varchar, PRIMARY KEY (first_name))
SQL: select first_name from professionals union select first_name from owners except select name from dogs