Show the people Id of the body builders.
select people_id from body_builder
Which people are there?
select * from people where people_id in (select people_id from body_builder)
What about people who are not there?
select * from people where people_id not in (select people_id from body_builder)
How many such people in total?
select count(*) from people where people_id not in (select people_id from body_builder)