오랑우탄의 반란

오늘도 오랑이는 문제를 풉니다.  1934. Confirmation Rate 조인을 활용해서 쉽게 풀 수 있는 문제입니다. SELECT s.user_id , round(ifnull(c2.confirm / c1.total,0),2) AS confirmation_rateFROM signups s left join (select user_id, count(*) as total from confirmations group by 1) c1 on s.user_id = c1.user_id left join (select user_id, count(*) as confirm from confirmations where action = 'confirmed' group by 1) c2 ..