From de4a0fa2ec2c560455bdfea071f15d6f513fa21c Mon Sep 17 00:00:00 2001
From: Alex <xarlama@bk.ru>
Date: Fri, 27 Feb 2026 15:31:56 +0300
Subject: [PATCH] PET task 4 fixed

---
 aharlamcev/PET-project_task4 | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 aharlamcev/PET-project_task4

diff --git a/aharlamcev/PET-project_task4 b/aharlamcev/PET-project_task4
new file mode 100644
index 0000000..5cb8fcd
--- /dev/null
+++ b/aharlamcev/PET-project_task4
@@ -0,0 +1,26 @@
+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
+						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 case when user_id in (select user_id from enrollments) then user_id end) as enrolled_users,
+		COUNT(distinct case when user_id in (select user_id from lesson_views) then user_id end) 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
+		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::numeric / users_in_cohort as avg_courses_per_user,
+avg_time_to_first_view
+from CTE