How many swimming records are there in the system?
select count(*) from record
What about that in terms of swimmer ids?
select swimmer_id, count(*) from record group by swimmer_id
Show me those with at least two.
select swimmer_id from record group by swimmer_id having count(*) >= 2
What about their names?
select t1.name from swimmer as t1 join record as t2 on t1.id = t2.swimmer_id group by t2.swimmer_id having count(*) >= 2