Написал витрину по курсам

gmokrousov/postgresql/DM_course_summary.sql

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+CREATE MATERIALIZED VIEW course_summary as 
+    with 
+        lw as (
+            select 
+                user_id,
+                lesson_id,
+                viewed_at 
+            from lesson_views
+        )
+    select
+        id as course_id,
+        title as course_title,
+        count(distinct e.user_id) as unique_users,
+        count(distinct l.lesson_id) as lessons_count,
+        count(distinct lw.viewed_at) as total_views,
+        round(count(distinct lw.viewed_at)::decimal / count(distinct e.user_id), 2) as avg_views_per_user,
+        min(lw.viewed_at) as first_viewed_at,
+        max(lw.viewed_at) as last_viewed_at 
+    from
+        courses as c 
+        join (select course_id, user_id from enrollments) as e on c.id = e.course_id 
+        join (select id as lesson_id, course_id from lessons) as l on c.id = l.course_id 
+        join lw on l.lesson_id = lw.lesson_id 
+    group by id;