Leetcode SQL (#595 – #597)

select 
name, 
population, 
area
from World
where area > 3000000 
or population > 25000000

select 
class
from courses
group by 1
having count(distinct student) >= 5

select 
round(ifnull(count(*)/requested,0),2) as accept_rate
from(
    select distinct 
    requester_id, 
    accepter_id
    from RequestAccepted
) a
join (
    select 
    count(*) as requested
    from(
        select distinct 
        sender_id, 
        send_to_id
        from FriendRequest
    ) f
) r on 1=1