4set 2번 문제

안녕하세요. 

아래 쿼리와 같이 SUM(CASE WHEN Status != 'completed'가 아닌

SUM(CASE WHEN Status = 'cancelled_by_driver ' 를 하면 틀린 답이라고 나옵니다.

같은 내용인거 같은데 왜 틀린지를 모르겠네요 ㅠ 확인해 주시면 감사하겠습니다. 

SELECT Day, ROUND(rate/total,2) AS `Cancellation Rate`

FROM (

SELECT a.Request_at AS Day

    , SUM(CASE WHEN Status = 'cancelled_by_driver ' THEN 1 ELSE 0 END) AS rate

    , COUNT(*) as total

FROM Trips a

    INNER JOIN Users uc ON a.Client_Id = uc.Users_Id

    INNER JOIN Users ud ON a.Driver_Id = ud.Users_Id

WHERE a.Request_at BETWEEN '2013-10-01' AND '2013-10-03'

AND uc.Banned = 'No'

AND ud.Banned = 'No'

GROUP BY 1  

) t