CREATE MATERIALIZED VIEW user_activity_summary AS
SELECT 
    u.id AS user_id,
    u.name,
    COUNT(DISTINCT e.course_id) AS enrollment_count,
    COUNT(DISTINCT lv.lesson_id) AS viewed_lessons_count,
    MAX(lv.viewed_at) AS last_viewed,
    MIN(lv.viewed_at) AS first_viewed,
    ROUND (
        CASE
            WHEN COUNT(DISTINCT l.id) = 0 THEN NULL
            ELSE COUNT(DISTINCT lv.lesson_id) * 1.0 / COUNT(DISTINCT l.id) * 100
        END, 2)::TEXT || '%' AS "engagement_rate"
FROM amaksatov.users u
LEFT JOIN enrollments e ON e.user_id = u.id
LEFT JOIN lessons l ON l.course_id = e.course_id
LEFT JOIN lesson_views lv ON lv.lesson_id = l.id AND u.id = lv.user_id
GROUP BY u.id
HAVING COUNT(e.id) > 0;