Monthly Active Users

Using a CTE, return the number of distinct active users per month as month ('YYYY-MM') and active_users, ordered by month.

Table schema

Activity(user_id INT, activity_date DATE)

Sample data

user_id | activity_date
1 | 2026-01-05
1 | 2026-01-20
2 | 2026-01-10
1 | 2026-02-03
3 | 2026-02-04
3 | 2026-02-09