added second part of pet project 'effective courses'

dmedvedev/11.2 Pet project Effective courses.sql

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+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
+