users-that-actively-request-confirmation-messages.sql

/*

Description
Table: Signups

https://leetcode.ca/2021-08-08-1939-Users-That-Actively-Request-Confirmation-Messages/

+----------------+----------+
| 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').
Write an SQL query to find the IDs of the users that requested a confirmation message twice within a 24-hour window. Two messages exactly 24 hours apart are considered to be within the window. The action does not affect the answer, only the request time.

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       | 2021-01-06 03:37:45 | timeout   |
| 7       | 2021-06-12 11:57:29 | confirmed |
| 7       | 2021-06-13 11:57:30 | confirmed |
| 2       | 2021-01-22 00:00:00 | confirmed |
| 2       | 2021-01-23 00:00:00 | timeout   |
| 6       | 2021-10-23 14:14:14 | confirmed |
| 6       | 2021-10-24 14:14:13 | timeout   |
+---------+---------------------+-----------+

Result table
+---------+
| user_id |
+---------+
| 2       |
| 3       |
| 6       |
+---------+

User 2 requested two messages within exactly 24 hours of each other, so we include them.
User 3 requested two messages within 6 minutes and 59 seconds of each other, so we include them.
User 6 requested two messages within 23 hours, 59 minutes, and 59 seconds of each other, so we include them.
User 7 requested two messages within 24 hours and 1 second of each other, so we exclude them from the answer.


*/

# V0
SELECT
DISTINCT c1.user_id As user_id
FROM
Confirmations AS c1
JOIN
Confirmations AS c2
ON
c1.user_id = c2.user_id
WHERE
c1.time_stamp < c2.time_stamp
AND
TIMESTAMPDIFF(SECOND, c1.time_stamp, c2.time_stamp) <  24*60*60
ORDER BY user_id

# V1
# https://blog.csdn.net/weixin_44171872/article/details/120108523
SELECT
DISTINCT c1.user_id As user_id
FROM
Confirmations AS c1
JOIN
Confirmations AS c2
ON
c1.user_id = c2.user_id
WHERE
c1.time_stamp < c2.time_stamp
AND
TIMESTAMPDIFF(SECOND, c1.time_stamp, c2.time_stamp) <  24*60*60
ORDER BY user_id

# V2
# Time:  O(nlogn)
# Space: O(n)
WITH confirmation_time_cte AS
  (SELECT user_id,
          TIMESTAMPDIFF(SECOND,
                        time_stamp,
                        LEAD(time_stamp, 1) OVER (PARTITION BY user_id
                                                  ORDER BY time_stamp)) AS time_diff
   FROM Confirmations)

SELECT DISTINCT user_id
FROM confirmation_time_cte
WHERE time_diff <= 86400;