CREATE MATERIALIZED VIEW user_activity_summary AS
SELECT
    u.id AS user_id, -- user_id
    u.name, -- name
    COUNT(DISTINCT e.course_id) AS enrollment_count, -- кол-во записей на курсы
    COUNT(DISTINCT lv.lesson_id) AS viewed_lessons_count, -- кол-во просмотренных уроков
    MAX(lv.viewed_at) AS last_viewed, -- последний просмотр
    MIN(lv.viewed_at) AS first_viewed, -- первый просмотр
    ROUND(COUNT(DISTINCT l.course_id) * 100.0 / COUNT(DISTINCT l.id), 2) || '%' AS engagement_rate -- вовлеченность(процент просмотренных/записанным)
FROM amaksatov.users u -- основная таблица
JOIN enrollments e ON e.user_id = u.id -- связь users с enrollments
LEFT JOIN lesson_views lv ON lv.user_id = e.user_id -- связь lessons с lesson_views
JOIN lessons l ON l.course_id = e.course_id  -- связь уроков с курсами пользователя
GROUP BY u.id, u.name -- группировка по user_id и name
ORDER BY user_id; -- сортировка по user_id


CREATE MATERIALIZED VIEW course_summary 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,
    COUNT(DISTINCT lv.id) AS total_views,
    ROUND(
        CASE
            WHEN COUNT(DISTINCT e.user_id) = 0 THEN NULL
            ELSE COUNT(DISTINCT lv.id) * 1.0 / COUNT(DISTINCT e.user_id)
        END, 2) AS avg_views_per_user,
    MIN(lv.viewed_at) AS first_viewed_at,
    MAX(lv.viewed_at) AS last_viewed_at
FROM courses c
LEFT JOIN enrollments e ON e.course_id = c.id
LEFT JOIN lessons l ON c.id = l.course_id
LEFT JOIN lesson_views lv ON lv.lesson_id = l.id
GROUP BY c.id;





CREATE MATERIALIZED VIEW platform_summary AS
WITH
user_stats AS (
    SELECT COUNT(*) AS total_users FROM users
),
course_stats AS (
    SELECT COUNT(*) AS total_courses FROM courses
),
lesson_stats AS (
    SELECT COUNT(*) AS total_lessons FROM lessons
),
view_stats AS (
    SELECT COUNT(*) AS total_views, COUNT(DISTINCT user_id) AS users_with_views
    FROM lesson_views
)

SELECT
    u.total_users,
    c.total_courses,
    l.total_lessons,
    v.users_with_views,

    ROUND(l.total_lessons::decimal / NULLIF(c.total_courses, 0), 2) AS avg_lessons_per_course,
    ROUND(v.total_views::decimal / NULLIF(l.total_lessons, 0), 2) AS avg_views_per_lesson

FROM user_stats u, course_stats c, lesson_stats l, view_stats v;