[597_EASY] Friend Requests I : Overall Acceptance Rate

Problem Description –

Write an SQL query to find the overall acceptance rate of requests, which is the number of acceptance divided by the number of requests. Return the answer rounded to 2 decimals places.

Note That –

1. The accepted requests are not necessarily from the table friend_request. In this case, Count the total accepted requests (no matter whether they are in the original requests), and divide it by the number of requests to get the acceptance rate.
2. It is possible that a sender sends multiple requests to the same receiver, and a request could be accepted more than once. In this case, the ‘duplicated’ requests or acceptances are only counted once.
3. If there are no requests at all, you should return 0.00 as the accept_rate.

The query result format is in the following example.

Follow up:

• Could you write a query to return the acceptance rate for every month?
• Could you write a query to return the cumulative acceptance rate for every day?

 

문제 풀이

sender가 동일한 수신자에게 여러번 요청을 보낼 수 있고, 요청이 두 번 이상 수락될 수 있기 때문에 DISTINCT하게 sender_id, send_to_id를 COUNT해야함 -- requester/accepter도 동일

 

소수점 이하 두자리 까지 반올림 -> round,2 

 

request가 전혀 없으면 accept_rate를 0으로 반환 -> ifnull 

 

 

SELECT(
	IFNULL(
    	ROUND(
        	(SELECT COUNT(DISTINCT requester_id, accepter_id) FROM RequestAccepted)/
                (SELECT COUNT(DISTINCT sender_id, send_to_id) FROM FriendRequest)
              ,2)
        ,0)
 ) AS accept_rate