Пэт проект по SQL

2026-01-23 21:49:18 +03:00
parent 2eac702d46
commit d32a9cb0a3
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 CREATE TABLE users (
    id INT PRIMARY KEY,
    name TEXT,
    age INT,
    email TEXT,
    registration_date DATE
 );
 INSERT INTO users VALUES
 (1, 'Alice', 25, 'alice@mail.com', '2023-01-10'),
 (2, 'Bob', 30, 'bob@gmail.com', '2023-02-05'),
 (3, 'Charlie', 22, 'charlie@mail.com', '2023-02-20'),
 (4, 'Diana', 28, 'diana@mail.com', '2023-03-01'),
 (5, 'Ethan', 35, 'ethan@gmail.com', '2023-03-10');
 SELECT * FROM users ORDER BY id;
 CREATE TABLE courses (
    id INT PRIMARY KEY,
    title TEXT,
    category TEXT,
    created_at DATE
 );
 INSERT INTO courses VALUES
 (1, 'SQL для начинающих', 'data', '2023-01-01'),
 (2, 'Python для анализа данных', 'programming', '2023-01-15'),
 (3, 'BI с нуля', 'business', '2023-03-01');
 SELECT * FROM courses ORDER BY id;
 CREATE TABLE lessons (
    id INT PRIMARY KEY,
    course_id INT,
    title TEXT,
    duration_min INT,
    FOREIGN KEY (course_id) REFERENCES courses(id)
 );
 INSERT INTO lessons VALUES
 (1, 1, 'SELECT и FROM', 10),
 (2, 1, 'JOIN', 15),
 (3, 2, 'Pandas', 20),
 (4, 3, 'Основы BI', 12),
 (5, 3, 'Метрики и дашборды', 18);
 SELECT * FROM lessons ORDER BY id;
 CREATE TABLE enrollments (
    id INT PRIMARY KEY,
    user_id INT,
    course_id INT,
    enrolled_at DATE,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (course_id) REFERENCES courses(id)
 );
 INSERT INTO enrollments VALUES
 (1, 1, 1, '2023-01-15'),
 (2, 1, 2, '2023-02-01'),
 (3, 2, 1, '2023-01-20'),
 (4, 3, 2, '2023-03-05'),
 (5, 4, 3, '2023-04-01');
 SELECT * FROM enrollments ORDER BY id;
 CREATE TABLE lesson_views (
    id INT PRIMARY KEY,
    user_id INT,
    lesson_id INT,
    viewed_at TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (lesson_id) REFERENCES lessons(id)
 );
 INSERT INTO lesson_views VALUES
 (1, 1, 1, '2023-01-16 10:00:00'),
 (2, 1, 2, '2023-01-16 10:15:00'),
 (3, 2, 1, '2023-01-21 09:00:00'),
 (4, 3, 3, '2023-03-06 12:00:00'),
 (5, 4, 4, '2023-04-02 10:00:00'),
 (6, 4, 5, '2023-04-03 10:00:00');
 SELECT * FROM lesson_views ORDER BY id;
 --Создаем materialized view c названием user_activity_summary
 DROP MATERIALIZED VIEW IF EXISTS user_activity_summary;
 CREATE MATERIALIZED VIEW user_activity_summary AS
 WITH
 enr AS (
  SELECT
    user_id,
    COUNT(*) AS enrollment_count
  FROM enrollments
  GROUP BY user_id
 ),
 views AS (
  SELECT
    user_id,
    COUNT(DISTINCT lesson_id) AS viewed_lessons_count,
    MIN(viewed_at) AS first_view,
    MAX(viewed_at) AS last_view
  FROM lesson_views
  GROUP BY user_id
 ),
 possible AS (
  SELECT
    e.user_id,
    COUNT(l.id) AS possible_lessons
  FROM enrollments e
  JOIN lessons l ON l.course_id = e.course_id
  GROUP BY e.user_id
 )
 SELECT
  u.id AS user_id,
  u.name,
  enr.enrollment_count,
  COALESCE(views.viewed_lessons_count, 0) AS viewed_lessons_count,
  views.last_view,
  views.first_view,
  ROUND(
    COALESCE(views.viewed_lessons_count, 0)::numeric
    / possible.possible_lessons * 100,
    2
  ) || '%' AS engagement_rate
 FROM users u
 JOIN enr ON enr.user_id = u.id
 JOIN possible ON possible.user_id = u.id
 LEFT JOIN views ON views.user_id = u.id
 ORDER BY u.id;
 --Проверка
 SELECT * FROM user_activity_summary ORDER BY user_id;
 --Создаем materialized view c названием course_summary
 DROP MATERIALIZED VIEW IF EXISTS course_summary;
 CREATE MATERIALIZED VIEW course_summary AS
 WITH
 -- 1) сколько уроков в каждом курсе
 lessons_cnt AS (
  SELECT
    course_id,
    COUNT(*) AS lessons_count
  FROM lessons
  GROUP BY course_id
 ),
 -- 2) сколько уникальных пользователей записано на курс
 users_cnt AS (
  SELECT
    course_id,
    COUNT(DISTINCT user_id) AS unique_users
  FROM enrollments
  GROUP BY course_id
 ),
 -- 3) просмотры по курсу (через lessons -> course_id)
 views_cnt AS (
  SELECT
    l.course_id,
    COUNT(lv.id) AS total_views,
    MIN(lv.viewed_at) AS first_viewed_at,
    MAX(lv.viewed_at) AS last_viewed_at
  FROM lessons l
  LEFT JOIN lesson_views lv ON lv.lesson_id = l.id
  GROUP BY l.course_id
 )
 SELECT
  c.id AS course_id,
  c.title AS course_title,
  COALESCE(u.unique_users, 0) AS unique_users,
  COALESCE(ls.lessons_count, 0) AS lessons_count,
  COALESCE(v.total_views, 0) AS total_views,
  ROUND(
    COALESCE(v.total_views, 0)::numeric / NULLIF(COALESCE(u.unique_users, 0), 0),
    2
  ) AS avg_views_per_user,
  v.first_viewed_at,
  v.last_viewed_at
 FROM courses c
 LEFT JOIN users_cnt u ON u.course_id = c.id
 LEFT JOIN lessons_cnt ls ON ls.course_id = c.id
 LEFT JOIN views_cnt v ON v.course_id = c.id
 ORDER BY c.id;
 SELECT * FROM course_summary ORDER BY course_id;
 --Создаем materialized view c названием platform_summary
 DROP MATERIALIZED VIEW IF EXISTS platform_summary;
 CREATE MATERIALIZED VIEW platform_summary AS
 SELECT
  (SELECT COUNT(*) FROM users) AS total_users,
  (SELECT COUNT(*) FROM courses) AS total_courses,
  (SELECT COUNT(*) FROM lessons) AS total_lessons,
  (SELECT COUNT(DISTINCT user_id) FROM lesson_views) AS users_with_views,
  ROUND(
    (SELECT COUNT(*) FROM lessons)::numeric
    / (SELECT COUNT(*) FROM courses),
    2
  ) AS avg_lessons_per_course,
  ROUND(
    (SELECT COUNT(*) FROM lesson_views)::numeric
    / (SELECT COUNT(*) FROM lessons),
    2
  ) AS avg_views_per_lesson;
  SELECT * FROM platform_summary;
 --Доп. задание: EXPLAIN
 EXPLAIN SELECT * FROM user_activity_summary;
 EXPLAIN SELECT * FROM course_summary;