30-Day Campaign User Retention

Task

You are given campaign interaction data and subsequent user activity data. Write a PostgreSQL query to calculate the 30-day retention rate for users who interacted with a specific Google Ads campaign. Treat a user as retained if they have at least one activity event in the 30 days after their first interaction with that campaign. Return the campaign name, the number of users in the campaign cohort, the number of retained users, and the retention rate as a percentage rounded to two decimals.