날짜를 내림차순으로 정렬하려고 했는데 뒤죽박죽이예요, 뭐가 문제인가요?

select * from checkins c 

inner join courses c2 on c.course_id = c2.course_id

inner join orders o on c.user_id = o.user_id 

where o.created_at >= '2020-08-01'

order by o.created_at desc