LeetCode-SQL-597. 好友申请 I ：总体通过率

select
round(
    ifnull(
    (select count(*) from (select distinct requester_id, accepter_id from request_accepted) as A)
    /
    (select count(*) from (select distinct sender_id, send_to_id from friend_request) as B),
    0)
, 2) as accept_rate;