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2688. Find Active Users

Description

Table: Users

+-------------+----------+ 
| Column Name | Type     | 
+-------------+----------+ 
| user_id     | int      | 
| item        | varchar  |
| created_at  | datetime |
| amount      | int      |
+-------------+----------+
There is no primary key in this table. The table may contain duplicate records. 
Each row includes the user ID, the purchased item, the date of purchase, and the purchase amount.

Write an SQL query that'll identify active users. An active user is a user that has made a second purchase within 7 days of any other of their purchases.

For example, if the ending date is May 31, 2023. So any date between May 31, 2023, and June 7, 2023 (inclusive) would be considered "within 7 days" of May 31, 2023.

Return a list of user_id which denotes the list of active users in any order.

The query result format is in the following example.

 

Example 1:

Input:
Users table:
+---------+-------------------+------------+--------+ 
| user_id | item              | created_at | amount |  
+---------+-------------------+------------+--------+
| 5       | Smart Crock Pot   | 2021-09-18 | 698882 |
| 6       | Smart Lock        | 2021-09-14 | 11487  |
| 6       | Smart Thermostat  | 2021-09-10 | 674762 |
| 8       | Smart Light Strip | 2021-09-29 | 630773 |
| 4       | Smart Cat Feeder  | 2021-09-02 | 693545 |
| 4       | Smart Bed         | 2021-09-13 | 170249 |
+---------+-------------------+------------+--------+ 
Output:
+---------+
| user_id | 
+---------+
| 6       | 
+---------+
Explanation: 
- User with user_id 5 has only one transaction, so he is not an active user.
- User with user_id 6 has two transaction his first transaction was on 2021-09-10 and second transation was on 2021-09-14. The distance between the first and second transactions date is <= 7 days. So he is an active user. 
- User with user_id 8 has only one transaction, so he is not an active user.  
- User with user_id 4 has two transaction his first transaction was on 2021-09-02 and second transation was on 2021-09-13. The distance between the first and second transactions date is > 7 days. So he is not an active user.

Solutions

  • # Write your MySQL query statement
SELECT
    DISTINCT user_id
FROM
    Users
WHERE
    user_id IN (
        SELECT
            user_id
        FROM
            (
                SELECT
                    user_id,
                    created_at,
                    lag(created_at, 1) over (
                        partition by user_id
                        ORDER BY
                            created_at
                    ) AS prev_created_at
                FROM
                    Users
            ) AS t
        WHERE
            DATEDIFF(created_at, prev_created_at) <= 7
    )

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