PET 2nd task completed

aharlamcev/postgresql/Pet-projectsql.sql

@@ -234,4 +234,42 @@ ROUND(100.0 * viewed_lessons_count / pl.poss_lessons, 2) as engagement_rate
 from viewed_count vc
 left join possible_lessons pl on vc.user_id = pl.user_id
 ;
-	
+
+------------------------------------------------------------------------------------------------------------------
+-- 2 задание Эффективность курсов
+
+create materialized view course_summary AS
+	with lessons_per_course as (
+								select c.id as course_id, c.title as course_title,
+								COUNT(distinct e.user_id) as unique_users,
+								COUNT(distinct l.id) as lessons_count
+								from courses c
+								left join enrollments e on c.id = e.course_id
+								join lessons l on e.course_id = l.course_id
+								group by c.id, c.title
+								),
+	course_views as (
+					select l.course_id, COUNT(lv.id) as total_views
+					from lesson_views lv
+					join lessons l on lv.lesson_id = l.id
+					group by l.course_id
+					),
+	view_date as (
+					select l.course_id,
+					MIN(lv.viewed_at) as first_viewed_at,
+					MAX(lv.viewed_at) as last_viewed_at
+					from lessons l
+					join lesson_views lv on l.id = lv.lesson_id
+					group by l.course_id
+					)
+	select lpc.course_id, lpc.course_title, lpc.unique_users, lpc.lessons_count,
+	ROUND(1.00 * cv.total_views / lpc.unique_users, 2) as avg_views_per_user,
+	vd.first_viewed_at,
+	vd.last_viewed_at
+	from lessons_per_course lpc
+	join course_views cv on lpc.course_id = cv.course_id
+	left join view_date vd on cv.course_id = vd.course_id
+	order by course_id
+;
+
+