Learn how to calculate monthly churn in PostgreSQL using a calendar CTE, active-user logic, NULL handling, and an anti-join.
Rahman
Posted on Sep 5
AI-assisted
Churn questions are common in data engineering and business intelligence interviews because they test more than basic aggregation. You need to work with time periods, define when a user is active, handle open-ended subscriptions, and compare one month with another.
I added this scenario to DataCurlew, where you can practice it directly in your browser. Let’s walk through the solution.
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