CREATE MATERIALIZED
VIEW conversion_funnel AS

-- CTE какое кол-во человек записалось на курс 
WITH

	enrolled_users
	AS
	(
		SELECT
			course_id,
			user_id,
			COUNT(*) OVER (PARTITION BY course_id) AS enrolled_count
		FROM pet_enrollments pe
	),

	-- СТЕ на начавших смотреть курс
	started_users
	AS
	(
		SELECT
			eu.course_id,
			COUNT(DISTINCT plv.user_id) AS started
		FROM enrolled_users eu -- Базой берем записанных пользователей
			LEFT JOIN pet_lessons pl
			ON eu.course_id = pl.course_id
			LEFT JOIN pet_lesson_views plv
			ON plv.lesson_id = pl.id AND plv.user_id = eu.user_id
		-- Проверяем, что смотрел именно записанный юзер
		GROUP BY eu.course_id
	),


	--СТЕ на кол-во просмотров курса и прогресс по курсу
	user_progress
	AS
	(
		SELECT
			eu.course_id,
			eu.user_id,
			COUNT(DISTINCT plv.lesson_id) * 1.0 / count_lesson_in_course.count_lesson_in_course AS progress
		FROM enrolled_users eu -- Базой берем записанных пользователей
			LEFT JOIN pet_lessons pl
			ON pl.course_id = eu.course_id
			LEFT JOIN pet_lesson_views plv
			ON plv.lesson_id = pl.id AND plv.user_id = eu.user_id -- Просмотры могут быть NULL, если записался, но не смотрел
			LEFT JOIN (
		SELECT
				pl.course_id,
				COUNT(*) AS count_lesson_in_course
			FROM pet_lessons pl
			GROUP BY pl.course_id
	) AS count_lesson_in_course
			ON count_lesson_in_course.course_id = eu.course_id
		GROUP BY eu.course_id, eu.user_id, count_lesson_in_course.count_lesson_in_course
	),

	main_table
	AS
	(
											SELECT
				pc.id AS course_id,
				pc.title AS course_title,
				'registered' AS stage_name,
				0 AS stage_order,
				(SELECT COUNT(*)
				FROM pet_users pu) AS users_count,
				ROUND(100, 2) || '%' AS conversion_from_previous,
				ROUND(100, 2) || '%' AS conversion_from_start

			FROM pet_courses pc

		UNION ALL

			SELECT
				pc.id AS course_id,
				pc.title AS course_title,
				'enrolled' AS stage_name,
				1 AS stage_order,
				COALESCE(eu.enrolled_count, 0),
				ROUND(COALESCE(eu.enrolled_count, 0) * 100.0 / NULLIF((SELECT COUNT(*) FROM pet_users), 0), 2) || '%' AS conversion_from_previous,
				ROUND(COALESCE(eu.enrolled_count, 0) * 100.0 / NULLIF((SELECT COUNT(*) FROM pet_users), 0), 2) || '%' AS conversion_from_start
			FROM pet_courses pc
				LEFT JOIN (SELECT course_id, MAX(enrolled_count) AS enrolled_count
				FROM enrolled_users
				GROUP BY course_id) eu
				ON eu.course_id = pc.id


		UNION ALL

			SELECT
				pc.id AS course_id,
				pc.title AS course_title,
				'started' AS stage_name,
				2 AS stage_order,
				COALESCE(su.started, 0),
				ROUND(COALESCE(su.started, 0) * 100.0 / NULLIF(eu.enrolled_count, 0), 2) || '%' AS conversion_from_previous,
				ROUND(COALESCE(su.started, 0) * 100.0 / NULLIF((SELECT COUNT(*) FROM pet_users), 0), 2) || '%' AS conversion_from_start
			FROM pet_courses pc
				LEFT JOIN (SELECT course_id, MAX(enrolled_count) AS enrolled_count
				FROM enrolled_users
				GROUP BY course_id) eu
				ON eu.course_id = pc.id
				LEFT JOIN started_users su
				ON su.course_id = pc.id

		UNION ALL

			SELECT
				pc.id AS course_id,
				pc.title AS course_title,
				'mid_progress' AS stage_name,
				3 AS stage_order,
				(SELECT COUNT(*)
				FROM user_progress up
				WHERE up.course_id = pc.id AND up.progress >= 0.5),
				ROUND((SELECT COUNT(*)
				FROM user_progress up
				WHERE up.course_id = pc.id AND up.progress >= 0.5) * 100.0 / NULLIF(su.started, 0), 2) || '%' AS conversion_from_previous,
				ROUND((SELECT COUNT(*)
				FROM user_progress up
				WHERE up.course_id = pc.id AND up.progress >= 0.5) * 100.0 / NULLIF((SELECT COUNT(*) FROM pet_users), 0), 2) || '%' AS conversion_from_start
			FROM pet_courses pc
				LEFT JOIN started_users su
				ON su.course_id = pc.id

		UNION ALL

			SELECT
				pc.id AS course_id,
				pc.title AS course_title,
				'completed' AS stage_name,
				4 AS stage_order,
				(SELECT COUNT(*)
				FROM user_progress up
				WHERE up.course_id = pc.id AND up.progress >= 1),
				ROUND((SELECT COUNT(*)
				FROM user_progress up
				WHERE up.course_id = pc.id AND up.progress >= 1) * 100.0 / NULLIF((SELECT COUNT(*) FROM user_progress up WHERE up.course_id = pc.id AND up.progress >= 0.5), 0), 2) || '%' AS conversion_from_previous,
				ROUND((SELECT COUNT(*)
				FROM user_progress up
				WHERE up.course_id = pc.id AND up.progress >= 1) * 100.0 / NULLIF((SELECT COUNT(*) FROM pet_users), 0), 2) || '%' AS conversion_from_start
			FROM pet_courses pc
	)
-- main select
SELECT
	course_id,
	course_title,
	stage_name,
	users_count,
	conversion_from_previous,
	conversion_from_start

FROM main_table
ORDER BY course_id, stage_order;