CREATE MATERIALIZED VIEW course_summary as 
    with 
        lw as (
            select 
                user_id,
                lesson_id,
                viewed_at 
            from lesson_views
        )
    select
        id as course_id,
        title as course_title,
        count(distinct e.user_id) as unique_users,
        count(distinct l.lesson_id) as lessons_count,
        count(distinct lw.viewed_at) as total_views,
        round(count(distinct lw.viewed_at)::decimal / count(distinct e.user_id), 2) as avg_views_per_user,
        min(lw.viewed_at) as first_viewed_at,
        max(lw.viewed_at) as last_viewed_at 
    from
        courses as c 
        join (select course_id, user_id from enrollments) as e on c.id = e.course_id 
        join (select id as lesson_id, course_id from lessons) as l on c.id = l.course_id 
        join lw on l.lesson_id = lw.lesson_id 
    group by id;