How many gymnasts are there?
select count(*) from gymnast as t1 join people as t2 on t1.gymnast_id = t2.people_id
How many gymnasts are there in each age group?
select t2.age, count(*) from gymnast as t1 join people as t2 on t1.gymnast_id = t2.people_id group by t2.age
How many gymnasts are there in each hometown?
select t2.hometown, count(*) from gymnast as t1 join people as t2 on t1.gymnast_id = t2.people_id group by t2.hometown