added three data_mart_files

skonev/postgresql/dm_course_summary.sql

@@ -0,0 +1,39 @@
+BEGIN;
+
+CREATE MATERIALIZED VIEW course_summary AS 
+WITH courses_users AS (
+SELECT 
+	c.id AS course_id,
+	c.title AS course_name,
+	COUNT(DISTINCT user_id) AS unique_users
+FROM courses c
+LEFT join enrollments e ON c.id = e.course_id 
+GROUP BY c.id, c.title
+), 
+courses_views AS (
+    SELECT 
+        l.course_id, 
+        COUNT(DISTINCT l.id) AS lessons_count,
+        COUNT(lv.id) AS total_views,
+        MAX(lv.viewed_at) AS last_viewed_at,
+        MIN(lv.viewed_at) AS first_viewed_at
+    FROM lessons l
+    JOIN lesson_views lv ON l.id = lv.lesson_id 
+    GROUP BY l.course_id
+)
+SELECT 
+	cu.course_id,
+	cu.course_name,
+	cu.unique_users,
+	cv.lessons_count,
+	cv.total_views,
+	ROUND(cv.total_views::DECIMAL / NULLIF(cu.unique_users, 0), 2) AS avg_views_per_user,
+	cv.first_viewed_at,
+	cv.last_viewed_at
+FROM courses_users cu
+LEFT JOIN courses_views cv USING(course_id)
+ORDER BY cu.course_id;
+
+COMMIT;
+
+

skonev/postgresql/dm_platform_summary.sql

@@ -0,0 +1,20 @@
+BEGIN;
+
+CREATE MATERIALIZED VIEW platform_summary AS 
+SELECT
+    (SELECT COUNT(*) FROM users) AS total_users,
+    (SELECT COUNT(*) FROM courses) AS total_courses,
+    (SELECT COUNT(*) FROM lessons) AS total_lessons,
+    (SELECT COUNT(DISTINCT user_id) FROM lesson_views) AS users_with_views,
+    ROUND(
+        (SELECT COUNT(*)::DECIMAL FROM lessons) / 
+        NULLIF((SELECT COUNT(DISTINCT course_id) FROM lessons), 0), 
+        2
+    ) AS avg_lessons_per_course,
+    ROUND(
+        (SELECT COUNT(*)::DECIMAL FROM lesson_views) / 
+        NULLIF((SELECT COUNT(DISTINCT lesson_id) FROM lesson_views), 0), 
+        2
+    ) AS avg_views_per_lesson;
+
+COMMIT;

skonev/postgresql/dm_user_activity_summary.sql

@@ -0,0 +1,38 @@
+BEGIN;
+
+CREATE MATERIALIZED VIEW user_activity_summary AS 
+WITH users_views AS (
+SELECT
+	u.id AS user_id,
+	u.name, 
+	COUNT(DISTINCT lv.lesson_id) AS viewed_lessons_COUNT,
+	MAX(lv.viewed_at) AS last_view,
+	MIN(lv.viewed_at) AS first_view
+FROM users AS u
+JOIN lesson_views AS lv on u.id = lv.user_id
+GROUP BY u.id
+
+),
+users_engagement AS (
+SELECT 
+	e.user_id AS user_id,
+	COUNT(l.id) AS lessons_cnt,
+	COUNT(DISTINCT course_id) AS enrollment_count
+FROM enrollments AS e
+JOIN lessons AS l using(course_id)
+GROUP BY e.user_id
+)
+
+SELECT 
+	uv.user_id,
+	uv.name,
+	ue.enrollment_count,
+	uv.viewed_lessons_count,
+	uv.lASt_view,
+	uv.first_view,
+	ROUND(uv.viewed_lessons_count::DECIMAL / NULLIF(ue.lessons_cnt, 0) * 100, 2)  AS engagement_rate
+FROM users_views AS uv
+LEFT JOIN users_engagement AS ue using (user_id)
+ORDER BY uv.user_id
+
+COMMIT;