create materialized view dm_course_summary as
select
	e.course_id,
	c.title,
	count(distinct e.user_id) as unique_users,
	count(distinct l.id) as lessons_count,
	count(distinct lv.id) as total_views,
	count(distinct lv.id)*1.0/count(distinct e.user_id) as avg_views_per_user,
	min(lv.viewed_at) as first_viewed_at,
	max(lv.viewed_at) as last_viewed_at
from enrollments e
join courses c on e.course_id = c.id
join lessons l on  c.id = l.course_id
join lessons_views lv on lv.lesson_id = l.id
group by e.course_id, c.title
order by e.course_id