Create 1934. Confirmation Rate.md

1934. Confirmation Rate.md

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+#### 1934. Confirmation Rate
+
+Table: Sig nups
+
+
+| 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.
+
+
+```sql
+SELECT s.user_id, ROUND(AVG(CASE WHEN c.action = 'confirmed' THEN 1 ELSE 0 END),2) AS confirmation_rate
+FROM signups s
+LEFT JOIN confirmation c ON s.user_id = c.user_id
+GROUP BY 1;
+```
+