From 93ae8af223a66b83d75e37b0076d9a76c8c055f1 Mon Sep 17 00:00:00 2001
From: Alex <xarlama@bk.ru>
Date: Thu, 19 Feb 2026 14:31:52 +0300
Subject: [PATCH] PET 4th task completed

---
 aharlamcev/postgresql/Pet-projectsql.sql | 33 ++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/aharlamcev/postgresql/Pet-projectsql.sql b/aharlamcev/postgresql/Pet-projectsql.sql
index bc21d74..1fb75f6 100644
--- a/aharlamcev/postgresql/Pet-projectsql.sql
+++ b/aharlamcev/postgresql/Pet-projectsql.sql
@@ -289,5 +289,38 @@ ROUND(1.00 * total_views / total_lessons, 2) as avg_views_per_lesson
 from total_counts
 ;
 
+-----------------------------------------------------------------------------------------------------
+-- 4 Задание Когортный анализ пользователей
+create materialized view user_cohort_analysis AS
+with needed_users as (
+						select distinct u.id as user_id, u.registration_date as reg_date, e.course_id, lv.id as view_id, 
+						lv.lesson_id as viewed_lesson_id, 
+						FIRST_VALUE(lv.viewed_at) over (partition by lv.user_id order by lv.viewed_at) as first_view_date,
+						e.user_id as enrolled_users,
+						lv.user_id as active_users
+						from users u
+						left join enrollments e on u.id = e.user_id
+						left join lesson_views lv on e.user_id = lv.user_id
+						order by user_id
+						),
+CTE as (
+		select 
+		TO_CHAR(reg_date, 'YYYY-MM') as cohort_month, 
+		COUNT(distinct user_id) as users_in_cohort,
+		COUNT(distinct enrolled_users) as enrolled_users,
+		COUNT(distinct active_users) as active_users,
+		COUNT(course_id) as courses_count,
+		extract('days' from AVG(first_view_date - reg_date)) as avg_time_to_first_view
+		from needed_users
+		where date_trunc('month', reg_date)::date = '2023-03-01'
+		group by cohort_month
+		)
+select cohort_month, users_in_cohort, enrolled_users, active_users,
+ROUND(100.0 * active_users / users_in_cohort, 2) as retention_rate,
+courses_count / users_in_cohort as avg_courses_per_user,
+avg_time_to_first_view
+from CTE
+;
+