What is the average age of all people?
select avg(age) from people
How about the average age of all gymnasts?
select avg(age) from gymnast as t1 join people as t2 on t1.gymnast_id = t2.people_id
Who is the youngest gymnast?
select t2.name from gymnast as t1 join people as t2 on t1.gymnast_id = t2.people_id order by t2.age asc limit 1
How many total points does he have?
select t1.total_points from gymnast as t1 join people as t2 on t1.gymnast_id = t2.people_id order by t2.age asc limit 1