1934. Confirmation Rate

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

Description

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.

ac