CREATE MATERIALIZED VIEW dm_user_activity_summary as 
with enrollment_counts as(
	select user_id, 
		   count(course_id) as enrollment_count
	from enrollments e
	group by user_id
),views as(
	select user_id, 
		count(distinct lesson_id) as viewed_lessons_count,
		min(viewed_at) as first_view, 
		max(viewed_at) as last_view
	from lessons_views
	group by user_id
), total_lessons as(
	select 	user_id, 
			count(*) as total_lessons
	from enrollments e
	join lessons using(course_id)
	group by user_id
	order by user_id
), engagment_rate as (
	select tl.user_id, round(v.viewed_lessons_count*100.0/nullif(total_lessons), 2) as engagment_rate
	from total_lessons tl
	join views v using(user_id) 
)
select u.id, u.name, enrollment_count, viewed_lessons_count, last_view, first_view, engagment_rate
from users u
join enrollment_counts ec on u.id = ec.user_id
join views v on u.id = v.user_id 
join engagment_rate er on u.id = er.user_id
order by u.id
/*
--первая попытка сделать витрину, делал избыточно с проверкой каждого подзапроса, поэтому забыл убрать order by, а также больше практиковался в оконных функциях
CREATE MATERIALIZED VIEW user_activity_summary as
with enrollment_counts as(
	select distinct user_id, 
		   count(course_id) over (partition by user_id) as enrollment_count
	from enrollments e
	order by user_id
), viewed_lessons_count as (
	select 
			user_id, count(distinct lesson_id) as viewed_lessons_count
	from lessons_views lv
	group by user_id
	order by user_id
), first_views as(
	select 
			user_id,
			viewed_at,
			row_number() over (partition by user_id order by viewed_at asc) as rnf
	from lessons_views
), last_views as(
	select 
			user_id,
			viewed_at,
			row_number() over (partition by user_id order by viewed_at desc) as rnl
	from lessons_views
), result_views as(
	select user_id, 
		fw.viewed_at as first_view, 
		lw.viewed_at as last_view
	from first_views fw
	join last_views lw using(user_id)
	where rnf = 1 and rnl = 1
), total_lessons as(
	select 	user_id, 
			count(*) as total_lessons
	from enrollments e
	join lessons using(course_id)
	group by user_id
	order by user_id
), engagment_rate as (
	select tl.user_id, round(vlc.viewed_lessons_count*100.0/total_lessons, 2) as engagment_rate
	from total_lessons tl
	join viewed_lessons_count vlc using(user_id) 
)
select u.id, u.name, enrollment_count, viewed_lessons_count, last_view, first_view, engagment_rate
from users u
join enrollment_counts ec on u.id = ec.user_id
join viewed_lessons_count vlc on u.id = vlc.user_id
join result_views rv on u.id = rv.user_id
join engagment_rate er on u.id = er.user_id
order by u.id
*/