Last question from easy set done today

Author: mrinal1704

Easy/Friend Requests 1.sql

@@ -0,0 +1,60 @@
+-- Question 49
+-- In social network like Facebook or Twitter, people send friend requests and accept others’ requests as well. Now given two tables as below:
+ 
+
+-- Table: friend_request
+-- | sender_id | send_to_id |request_date|
+-- |-----------|------------|------------|
+-- | 1         | 2          | 2016_06-01 |
+-- | 1         | 3          | 2016_06-01 |
+-- | 1         | 4          | 2016_06-01 |
+-- | 2         | 3          | 2016_06-02 |
+-- | 3         | 4          | 2016-06-09 |
+ 
+
+-- Table: request_accepted
+-- | requester_id | accepter_id |accept_date |
+-- |--------------|-------------|------------|
+-- | 1            | 2           | 2016_06-03 |
+-- | 1            | 3           | 2016-06-08 |
+-- | 2            | 3           | 2016-06-08 |
+-- | 3            | 4           | 2016-06-09 |
+-- | 3            | 4           | 2016-06-10 |
+ 
+
+-- Write a query to find the overall acceptance rate of requests rounded to 2 decimals, which is the number of acceptance divide the number of requests.
+ 
+
+-- For the sample data above, your query should return the following result.
+ 
+
+-- |accept_rate|
+-- |-----------|
+-- |       0.80|
+ 
+
+-- Note:
+-- The accepted requests are not necessarily from the table friend_request. In this case, you just need to simply 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.
+-- 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.
+-- If there is no requests at all, you should return 0.00 as the accept_rate.
+ 
+
+-- Explanation: There are 4 unique accepted requests, and there are 5 requests in total. 
+-- So the rate is 0.80.
+
+-- Solution
+with t1 as
+(
+	select distinct sender_id, send_to_id
+	from friend_request
+), t2 as
+(
+	select distinct requester_id, accepter_id
+	from request_accepted
+)
+
+Select 
+ifnull((
+        select distinct
+        round((select count(*) from t2) / ( select count(*) from t1),2) from t1,t2
+    ),0) 'accept_rate'