why this line in status table mean active user? this is solution of code academy. this lesson really lack of explaination.
part 3 of lesson, link course : https://www.codecademy.com/paths/data-science/tracks/analyze-data-sql-analyze-real-data/modules/analyze-data-sql-user-churn/lessons/churn-rates-les/exercises/single-month-ii
WHEN subscription_end >= ‘2017-01-01’ (why this line mean active user?)
subscription_end IS NULL
END as is_active