/* 
- ВИТРИНА ДЛЯ АНАЛИЗА КОНВЕРСИИ ПРОХОЖДЕНИЯ КУРСА ПОЛЬЗОВАТЕЛЯМИ
- CORE.DIM_USER И CORE.FACT_LESSON_VIEWS DISTRIBUTED BY (user_id)
- ИТОГОВОЕ РАСПРЕДЕЛЕНИЕ ПО (user_id, course_id)
*/

CREATE MATERIALIZED VIEW IF NOT EXISTS dm.course_completion_rate AS
WITH t1 AS (
SELECT
	e.user_id,
	du.name AS user_name,
	e.course_id, 
	dc.title AS course_title,
	COUNT(DISTINCT dl.lesson_id) AS lessons_in_course
FROM core.enrollments e
JOIN core.dim_user du USING (user_id)
JOIN core.dim_course dc USING (course_id)
LEFT JOIN core.dim_lesson dl USING (course_id)
GROUP BY user_id, du.name, course_id, dc.title
),
t2 AS (
SELECT 
	user_id,
	course_id,
	COUNT(DISTINCT lesson_id) AS lessons_viewed
FROM core.fact_lesson_views
GROUP BY user_id, course_id
)

SELECT 
	t1.user_id,
	t1.user_name,
	t1.course_id,
	t1.course_title,
	t1.lessons_in_course,
	COALESCE(t2.lessons_viewed, 0) AS lessons_viewed,
	COALESCE(ROUND(lessons_viewed::DECIMAL / NULLIF(lessons_in_course, 0), 2), 0) AS completion_rate
FROM t1 
LEFT JOIN t2 USING (user_id, course_id)
DISTRIBUTED BY (user_id, course_id);