1934.(Medium)Confirmation Rate

Table: Signups

+----------------+----------+
| Column Name    | Type     |
+----------------+----------+
| user_id        | int      |
| time_stamp     | datetime |
+----------------+----------+
user_id is the primary key for this table.
Each row contains information about the signup time for the user with ID user_id.

Table: Confirmations

+----------------+----------+
| Column Name    | Type     |
+----------------+----------+
| user_id        | int      |
| time_stamp     | datetime |
| action         | ENUM     |
+----------------+----------+
(user_id, time_stamp) is the primary key for this table.
user_id is a foreign key with a reference to the Signups table.
action is an ENUM of the type ('confirmed', 'timeout')
Each row of this table indicates that the user with ID user_id requested a confirmation message at time_stamp and that confirmation message was either confirmed ('confirmed') or expired without confirming ('timeout').

The confirmation rate of a user is the number of 'confirmed' messages divided by the total number of requested confirmation messages. The confirmation rate of a user that did not request any confirmation messages is 0. Round the confirmation rate to two decimal places.

Write an SQL query to find the confirmation rate of each user.

Return the result table in any order.

The query result format is in the following example:

Signups table:
+---------+---------------------+
| user_id | time_stamp          |
+---------+---------------------+
| 3       | 2020-03-21 10:16:13 |
| 7       | 2020-01-04 13:57:59 |
| 2       | 2020-07-29 23:09:44 |
| 6       | 2020-12-09 10:39:37 |
+---------+---------------------+

Confirmations table:
+---------+---------------------+-----------+
| user_id | time_stamp          | action    |
+---------+---------------------+-----------+
| 3       | 2021-01-06 03:30:46 | timeout   |
| 3       | 2021-07-14 14:00:00 | timeout   |
| 7       | 2021-06-12 11:57:29 | confirmed |
| 7       | 2021-06-13 12:58:28 | confirmed |
| 7       | 2021-06-14 13:59:27 | confirmed |
| 2       | 2021-01-22 00:00:00 | confirmed |
| 2       | 2021-02-28 23:59:59 | timeout   |
+---------+---------------------+-----------+

Result table
+---------+-------------------+
| user_id | confirmation_rate |
+---------+-------------------+
| 6       | 0.00              |
| 3       | 0.00              |
| 7       | 1.00              |
| 2       | 0.50              |
+---------+-------------------+

User 6 did not request any confirmation messages. The confirmation rate is 0.
User 3 made 2 requests and both timed out. The confirmation rate is 0.
User 7 made 3 requests and all were confirmed. The confirmation rate is 1.
User 2 made 2 requests where one was confirmed and the other timed out. The confirmation rate is 1 / 2 = 0.5.

来源：力扣（LeetCode）

链接：https://leetcode-cn.com/problems/confirmation-rate

著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

Solution

SELECT user_id
	, ROUND(IFNULL(sum(action='confirmed'),0)/count(1),2) confirmation_rate
FROM Signups s LEFT JOIN Confirmations c USING(user_id)
GROUP BY user_id;

Schema

Create table If Not Exists Signups (user_id int, time_stamp datetime);
Create table If Not Exists Confirmations (user_id int, time_stamp datetime, action ENUM('confirmed','timeout'));
Truncate table Signups;
insert into Signups (user_id, time_stamp) values ('3', '2020-03-21 10:16:13');
insert into Signups (user_id, time_stamp) values ('7', '2020-01-04 13:57:59');
insert into Signups (user_id, time_stamp) values ('2', '2020-07-29 23:09:44');
insert into Signups (user_id, time_stamp) values ('6', '2020-12-09 10:39:37');
Truncate table Confirmations;
insert into Confirmations (user_id, time_stamp, action) values ('3', '2021-01-06 03:30:46', 'timeout');
insert into Confirmations (user_id, time_stamp, action) values ('3', '2021-07-14 14:00:00', 'timeout');
insert into Confirmations (user_id, time_stamp, action) values ('7', '2021-06-12 11:57:29', 'confirmed');
insert into Confirmations (user_id, time_stamp, action) values ('7', '2021-06-13 12:58:28', 'confirmed');
insert into Confirmations (user_id, time_stamp, action) values ('7', '2021-06-14 13:59:27', 'confirmed');
insert into Confirmations (user_id, time_stamp, action) values ('2', '2021-01-22 00:00:00', 'confirmed');
insert into Confirmations (user_id, time_stamp, action) values ('2', '2021-02-28 23:59:59', 'timeout');