1454. Active Users 🔒

Description

Table: Accounts

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| name          | varchar |
+---------------+---------+
id is the primary key (column with unique values) for this table.
This table contains the account id and the user name of each account.

Table: Logins

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| login_date    | date    |
+---------------+---------+
This table may contain duplicate rows.
This table contains the account id of the user who logged in and the login date. A user may log in multiple times in the day.

Active users are those who logged in to their accounts for five or more consecutive days.

Write a solution to find the id and the name of active users.

Return the result table ordered by id.

The result format is in the following example.

Example 1:

Input: 
Accounts table:
+----+----------+
| id | name     |
+----+----------+
| 1  | Winston  |
| 7  | Jonathan |
+----+----------+
Logins table:
+----+------------+
| id | login_date |
+----+------------+
| 7  | 2020-05-30 |
| 1  | 2020-05-30 |
| 7  | 2020-05-31 |
| 7  | 2020-06-01 |
| 7  | 2020-06-02 |
| 7  | 2020-06-02 |
| 7  | 2020-06-03 |
| 1  | 2020-06-07 |
| 7  | 2020-06-10 |
+----+------------+
Output: 
+----+----------+
| id | name     |
+----+----------+
| 7  | Jonathan |
+----+----------+
Explanation: 
User Winston with id = 1 logged in 2 times only in 2 different days, so, Winston is not an active user.
User Jonathan with id = 7 logged in 7 times in 6 different days, five of them were consecutive days, so, Jonathan is an active user.

Follow up: Could you write a general solution if the active users are those who logged in to their accounts for n or more consecutive days?

Solutions

Solution 1: Using Window Functions

First, we join the Logins table and the Accounts table, and remove duplicates to get the temporary table T.

Then, we use the window function ROW_NUMBER() to calculate the base login date g for each user id. If a user logs in for 5 consecutive days, their g values are the same.

Finally, we group by id and g to count the number of logins for each user. If the number of logins is greater than or equal to 5, then the user is considered active.

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# Write your MySQL query statement below
WITH
    T AS (
        SELECT DISTINCT *
        FROM
            Logins
            JOIN Accounts USING (id)
    ),
    P AS (
        SELECT
            *,
            DATE_SUB(
                login_date,
                INTERVAL ROW_NUMBER() OVER (
                    PARTITION BY id
                    ORDER BY login_date
                ) DAY
            ) g
        FROM T
    )
SELECT DISTINCT id, name
FROM P
GROUP BY id, g
HAVING COUNT(*) >= 5
ORDER BY 1;

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