CREATE database pet;

-- Этап 1
-- Задание 1
-- Перенести данные как в пет-проекте с Greenplum

-- Создаем таблицы, чтобы потом загрузить в них данные из таблиц GreenPlum

-- Таблица user из GP

CREATE TABLE pet.core_user (
    user_id Int32,
    name String,
    age Int32,
    email String,
    registration_date DateTime64(3, 'UTC')
)
ENGINE = MergeTree
ORDER BY user_id;

-- Таблица course из GP
CREATE TABLE pet.core_course (
    course_id Int32,
    title String,
    category String
)
ENGINE = MergeTree
ORDER BY course_id;

-- Таблица lesson из GP
CREATE TABLE pet.core_lesson (
    lesson_id Int32,
    title String,
    duration_min Int32,
    course_id Int32
)
ENGINE = MergeTree
ORDER BY lesson_id;

-- Таблица fact_lesson_views из GP

CREATE TABLE pet.core_fact_lesson_views (
    user_id Int32, 
    lesson_id Int32,
    course_id Int32,
    viewed_at DateTime64(3, 'UTC')
)
ENGINE = MergeTree
ORDER BY user_id;

-- Таблица enrollments из GP

CREATE TABLE pet.core_enrollments (
    user_id Int32,
    course_id Int32,
    enrolled_at DateTime64(3, 'UTC')
)
ENGINE = MergeTree
ORDER BY user_id;

-- Этап 2. Создание витринных таблиц
-- Задание 2: Подготовь структуру витрины lesson_popularity_summary

-- Создаем пустую таблицу lesson_popularity_summary(структуру витрины)

CREATE TABLE pet.lesson_popularity_summary
(
    lesson_id     UInt32,
    lesson_title  String,
    course_id     UInt32,
    course_title  String,
    total_views   UInt32,
    unique_users  UInt32,
    first_view    DateTime64(3, 'UTC'),
    last_view     DateTime64(3, 'UTC')
)
ENGINE = MergeTree
ORDER BY (lesson_id, course_id);

-- Создаем Materialized View

CREATE MATERIALIZED VIEW pet.mv_lesson_popularity_summary
TO pet.lesson_popularity_summary
AS
SELECT
    flv.lesson_id AS lesson_id,
    l.title AS lesson_title,
    flv.course_id AS course_id,
    c.title AS course_title,
    count() AS total_views,
    uniqExact(flv.user_id) AS unique_users,
    min(flv.viewed_at) AS first_view,
    max(flv.viewed_at) AS last_view
FROM pet.core_fact_lesson_views AS flv
JOIN pet.core_lesson  AS l ON flv.lesson_id = l.lesson_id
JOIN pet.core_course  AS c ON flv.course_id = c.course_id
GROUP BY
    flv.lesson_id,
    l.title,
    flv.course_id,
    c.title;

-- Вставляем данные в таблицу pet.lesson_popularity_summary

INSERT INTO pet.lesson_popularity_summary
SELECT
    flv.lesson_id,
    l.title AS lesson_title,
    flv.course_id,
    c.title AS course_title,
    count() AS total_views,
    uniqExact(flv.user_id) AS unique_users,
    min(flv.viewed_at) AS first_view,
    max(flv.viewed_at) AS last_view
FROM pet.core_fact_lesson_views AS flv
JOIN pet.core_lesson  AS l ON flv.lesson_id = l.lesson_id
JOIN pet.core_course  AS c ON flv.course_id = c.course_id
GROUP BY
    flv.lesson_id,
    l.title,
    flv.course_id,
    c.title;

-- Задание 3: Создай витрину inactive_users_summary

-- Создаем пустую таблицу inactive_users_summary(структуру витрины)

CREATE TABLE pet.inactive_users_summary
(
    user_id UInt32,
    name String,
    email String,
    age UInt8,
    registered_courses_count UInt32,
    registration_date DateTime64(3, 'UTC')
)
ENGINE = MergeTree
ORDER BY (user_id);

-- Создаем Materialized View

CREATE MATERIALIZED VIEW pet.mv_inactive_users_summary
TO pet.inactive_users_summary
AS
SELECT
    u.user_id AS user_id,
    u.name AS name,
    u.email AS email,
    u.age AS age,
    countDistinct(e.course_id) AS registered_courses_count,
    u.registration_date AS registration_date
FROM pet.core_user AS u
LEFT JOIN pet.core_enrollments AS e ON u.user_id = e.user_id
WHERE u.user_id NOT IN (
    SELECT DISTINCT user_id
    FROM pet.core_fact_lesson_views
)
GROUP BY
    u.user_id,
    u.name,
    u.email,
    u.age,
    u.registration_date;

-- Вставляем данные в таблицу inactive_users_summary

INSERT INTO pet.inactive_users_summary
SELECT
    u.user_id,
    u.name,
    u.email,
    u.age,
    countDistinct(e.course_id) AS registered_courses_count,
    u.registration_date
FROM pet.core_user AS u
LEFT JOIN pet.core_enrollments AS e
    ON u.user_id = e.user_id
WHERE u.user_id NOT IN (               
    SELECT DISTINCT user_id
    FROM pet.core_fact_lesson_views
)
/*
 * этот подзапрос WHERE... просто выбрасывает всех, кто хоть раз что‑то посмотрел,
 * независимо от количества строк и особенностей JOIN’ов.
 */
GROUP BY
    u.user_id,
    u.name,
    u.email,
    u.age,
    u.registration_date;


-- Задание 4: Создай витрину course_completion_rate

CREATE TABLE pet.course_completion_rate
(
    user_id          UInt32,
    user_name        String,
    course_id        UInt32,
    course_title     String,
    lessons_in_course UInt32,
    lessons_viewed    UInt32,
    completion_rate   Float32
)
ENGINE = MergeTree
ORDER BY (user_id, course_id);

-- Создаем Materialized View

CREATE MATERIALIZED VIEW pet.mv_course_completion_rate
TO pet.course_completion_rate
AS
SELECT
    u.user_id AS user_id,
    u.name AS user_name,
    c.course_id AS course_id,
    c.title AS course_title,
    countDistinct(l.lesson_id) AS lessons_in_course,
    countDistinct(flv.lesson_id) AS lessons_viewed,
    if(countDistinct(l.lesson_id) = 0,0,
       round(countDistinct(flv.lesson_id) * 1.0 / countDistinct(l.lesson_id),2)
    ) AS completion_rate
FROM pet.core_enrollments AS e
JOIN pet.core_user      AS u ON e.user_id   = u.user_id
JOIN pet.core_course    AS c ON e.course_id = c.course_id
JOIN pet.core_lesson    AS l ON c.course_id = l.course_id
LEFT JOIN pet.core_fact_lesson_views AS flv
       ON flv.user_id   = e.user_id
      AND flv.course_id = e.course_id
GROUP BY
    u.user_id,
    u.name,
    c.course_id,
    c.title;

-- Вставляем данные в таблицу pet.course_completion_rate
INSERT INTO pet.course_completion_rate
-- Создаем две временные таблицы:
-- 1) Сколько уроков в каждом курсе
WITH
lessons_per_course AS (
    SELECT
        course_id,
        countDistinct(lesson_id) AS lessons_in_course
    FROM pet.core_lesson
    GROUP BY course_id
),
-- 2) Сколько уроков каждого курса посмотрел пользователь
views_per_user_course AS (
    SELECT
        user_id,
        course_id,
        countDistinct(lesson_id) AS lessons_viewed
    FROM pet.core_fact_lesson_views
    GROUP BY user_id, course_id
)
-- Основной запрос
SELECT
    u.user_id,
    u.name AS user_name,
    c.course_id,
    c.title AS course_title,
    lpc.lessons_in_course,
    coalesce(vpc.lessons_viewed, 0) AS lessons_viewed,
    ROUND(
        COALESCE(
            NULLIF(coalesce(vpc.lessons_viewed, 0) * 1.0, 0)
            / NULLIF(lpc.lessons_in_course * 1.0, 0),
            0
        ),
        2
    ) AS completion_rate
FROM pet.core_user AS u
JOIN pet.core_enrollments AS e ON u.user_id  = e.user_id
JOIN pet.core_course AS c ON e.course_id = c.course_id
JOIN lessons_per_course AS lpc ON c.course_id = lpc.course_id
LEFT JOIN views_per_user_course AS vpc ON vpc.user_id   = u.user_id AND vpc.course_id = c.course_id
ORDER BY
    u.user_id,
    c.course_id;