add pet-project

dmezentsev/postgresql/pet_project/dm_course_summary.sql

@@ -0,0 +1,46 @@
+DROP MATERIALIZED VIEW IF EXISTS dmezentsev.course_summary;
+CREATE MATERIALIZED VIEW dmezentsev.course_summary AS
+WITH count_users AS (
+	-- Кол-во уникальных пользователей в курсах
+	SELECT
+        c.id AS course_id,
+		c.title AS course_title,
+		COUNT(DISTINCT e.user_id) AS unique_users
+	FROM dmezentsev.courses c 
+	LEFT JOIN dmezentsev.enrollments e ON c.id = e.course_id
+	GROUP BY c.id, c.title
+),
+	count_lessons AS (
+	-- Кол-во уроков в курсах
+	SELECT
+        course_id,
+		COUNT(id) AS lessons_count
+	FROM dmezentsev.lessons 
+	GROUP BY course_id
+),
+	views_count AS (
+	-- Суммарное число просмотров по каждому курсу 
+	SELECT 
+        l.course_id,
+		COUNT(lv.id) AS total_views,
+		MIN(lv.viewed_at) AS first_viewed_at,
+		MAX(lv.viewed_at) AS last_viewed_at
+	FROM dmezentsev.lessons l 
+	LEFT JOIN dmezentsev.lesson_views lv  ON l.id = lv.lesson_id
+	GROUP BY l.course_id
+)
+
+SELECT
+    cu.course_id,
+	cu.course_title,
+	cu.unique_users,
+	cl.lessons_count,
+	vc.total_views,
+	ROUND(COALESCE(vc.total_views::numeric / 
+		cu.unique_users, 0), 2) AS avg_views_per_user,
+	vc.first_viewed_at,
+	vc.last_viewed_at
+FROM count_users cu 
+LEFT JOIN count_lessons cl USING (course_id)
+LEFT JOIN views_count vc USING (course_id)
+ORDER BY cu.course_id;