Question

1934. Confirmation Rate

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Description

Table: Signups

+----------------+----------+
| Column Name  | Type   |
+----------------+----------+
| user_id    | int    |
| time_stamp   | datetime |
+----------------+----------+
user_id is the column of unique values 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 (combination of columns with unique values) for this table.
user_id is a foreign key (reference column) to the Signups table.
action is an ENUM (category) 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 a solution to find the confirmation rate of each user.

Return the result table in any order.

The result format is in the following example.

 

Example 1:

Input: 
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   |
+---------+---------------------+-----------+
Output: 
+---------+-------------------+
| user_id | confirmation_rate |
+---------+-------------------+
| 6     | 0.00        |
| 3     | 0.00        |
| 7     | 1.00        |
| 2     | 0.50        |
+---------+-------------------+
Explanation: 
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.

Solutions

Solution 1: Left Join + Grouping

We can use a left join to join the Signups table and the Confirmations table on user_id, and then use GROUP BY to group by user_id for aggregation.

# Write your MySQL query statement below
SELECT
  user_id,
  ROUND(IFNULL(SUM(action = 'confirmed') / COUNT(1), 0), 2) AS confirmation_rate
FROM
  SignUps
  LEFT JOIN Confirmations USING (user_id)
GROUP BY 1;