CREATE MATERIALIZED VIEW course_summary AS

--кол-во уникальных пользователей в рамках одного курса (ready)
WITH unique_users AS (
	SELECT 
		pe.course_id,
		COUNT(*) AS unique_users
	FROM pet_enrollments pe
	GROUP BY pe.course_id 
	ORDER BY pe.course_id 
),

--общее кол-во уроков
	lesson_count AS (
	SELECT 
		pl.course_id,
		COUNT(*) AS lesson_count
	FROM pet_lessons pl		
	GROUP BY pl.course_id
	ORDER BY pl.course_id 

),

--суммарное число просмотров уроков по курсу
total_views AS (
	SELECT 
		pc.id,
		COUNT(*) AS total_views
	FROM pet_courses pc
	JOIN pet_lessons pl ON pc.id = pl.course_id
	JOIN pet_lesson_views plv ON pl.id = plv.lesson_id
	GROUP BY pc.id
	ORDER BY pc.id

),

--дата и время первого просмотра любого урока курса
first_viewed_at AS (
	SELECT 
		pc.id,
		FIRST_VALUE(plv.viewed_at) OVER (
			PARTITION BY pc.id
			ORDER BY plv.viewed_at
		) AS first_viewed_at
	FROM pet_courses pc
	JOIN pet_lessons pl ON pc.id = pl.course_id
	JOIN pet_lesson_views plv ON pl.id = plv.lesson_id
),

--дата и время последнего просмотра любого урока курса
last_viewed_at AS (
	SELECT 
		pc.id,
		LAST_VALUE(plv.viewed_at) OVER (
			PARTITION BY pc.id
			ORDER BY plv.viewed_at
			ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
		) AS last_viewed_at
	FROM pet_courses pc
	JOIN pet_lessons pl ON pc.id = pl.course_id
	JOIN pet_lesson_views plv ON pl.id = plv.lesson_id
)

SELECT 
	pc.id AS course_id,
	pc.title AS course_title,
	uu.unique_users,
	lc.lesson_count,
	tv.total_views,
	ROUND(tv.total_views * 1.0 / uu.unique_users, 2) AS avg_views_per_user,
	first_viewed_at,
	last_viewed_at

FROM pet_courses pc 
LEFT JOIN unique_users uu ON pc.id = uu.course_id
LEFT JOIN lesson_count lc ON lc.course_id = pc.id 
LEFT JOIN total_views tv ON tv.id = pc.id
LEFT JOIN first_viewed_at fva ON fva.id = pc.id 
LEFT JOIN last_viewed_at lva ON lva.id = pc.id 

GROUP BY pc.id, uu.unique_users, lc.lesson_count, tv.total_views, first_viewed_at, last_viewed_at
ORDER BY course_id;