SQL Retention Over 90 Days

Write a SQL query to calculate the retention rate of users who engaged with a specific document category over the last 90 days at Scribd. Treat a user as retained if they have another Scribd engagement within 30 days after their first engagement with the category. Exclude users whose first category engagement occurred less than 30 days ago, because their retention window is incomplete.

Output

1. Return one row for the Audiobooks category.
2. Include category_name, cohort_users, retained_users, and retention_rate as a percentage rounded to two decimal places.
3. Include only users with a complete 30-day retention window.