mnoskov/postgresql/Пет-проект: Онлайн-курсы/2. Создание отчетности (витрин)/DQL_materialized_view_reporting_on_interactions.sql

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+CREATE MATERIALIZED VIEW platform_summary as
+WITH users_count AS (
+	SELECT
+		count(*) AS total_users
+	FROM
+		users
+),
+courses_count AS (
+	SELECT
+		count(*) AS total_courses
+	FROM
+		courses
+),
+lessons_count AS (
+	SELECT
+		count(*) AS total_lessons
+	FROM
+		lessons
+),
+users_with_views AS (
+	SELECT
+		count(distinct user_id) AS users_with_views
+	FROM
+		lesson_views
+),
+views_count AS (
+	SELECT
+		count(*) AS total_views
+	FROM
+		lesson_views lv
+)
+SELECT
+	uc.total_users,
+	cc.total_courses,
+	lc.total_lessons,
+	uwv.users_with_views,
+	round(lc.total_lessons / cc.total_courses::NUMERIC, 2) AS avg_lessons_per_course,
+	round(vc.total_views / lc.total_lessons::NUMERIC, 2) AS avg_views_per_lesson
+FROM
+	users_count uc
+CROSS JOIN
+	courses_count cc
+CROSS JOIN
+	lessons_count lc
+CROSS JOIN
+	users_with_views uwv
+CROSS JOIN
+	views_count AS vc;