How old is David Butler?
select age from people where name = "David Butler"
Where does he work?
select t3.name from employment as t1 join people as t2 on t1.people_id = t2.people_id join company as t3 on t1.company_id = t3.company_id where t2.name = "Brad Lohaus"
Tell me the names of people that are not employed by any company.
select name from people where people_id not in (select people_id from employment)