How many persons are on the list?
select count ( * ) from person
Who is the least aged person on the list?
select name from person order by age limit 1
How many people whose age is greater 30 and job is engineer?
select count ( * ) from person where age > 30 and job = 'engineer'
How many female people are on the list?
select count ( * ) from person where gender = 'female'