Six-Month User Retention Cohorts

Task

You are given user signup data and Nykaa app activity logs. Write a PostgreSQL query to calculate monthly cohort retention for the first six months after signup. Each cohort is defined by the user's signup month, and a user is retained in month n if they have at least one activity event in the nth month after their signup month. Return the cohort month, cohort size, retained users for months 0 through 5, and retention percentages for those months.

Use the signup month from users.created_at, count only users from the Nykaa App surface, and ignore activity rows where event_date is NULL.