Skypro sells online data-analyst courses and each morning the dashboard shows how many students are currently in active learning. Every enrollment carries an enrollment_period of type DATERANGE — start date inclusive, end date exclusive ('[)'). Table user_courses: - user_id — student id - course_id — course id - enrollment_period DATERANGE — access window Count how many distinct students had at least one active enrollment period covering 2024-04-15. Each student is counted once even if they have several active courses at the same time.