Пэт проект по SQL

2026-01-23 21:49:18 +03:00
parent 2eac702d46
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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;
+  
+  
+