Merge pull request 'Решение по базовый SQL' (#39) from ebelykh into main

Reviewed-on: https://gitea.de-infra.servehttp.com/de-infrastructure/DWH/pulls/39

ebelykh/postgresql/JOIN/JOIN.sql

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+--Задача 1068
+SELECT p.product_name, s.year, s.price
+FROM Sales s
+JOIN Product p
+ON s.product_id = p.product_id;
+
+--Задача 1378
+SELECT EmployeeUNI.unique_id,
+       Employees.name
+FROM Employees
+LEFT JOIN EmployeeUNI
+ON Employees.id = EmployeeUNI.id;      
+
+--Задача 577
+SELECT e.name, b.bonus
+FROM Employee e
+LEFT JOIN Bonus b
+ON e.empId = b.empId
+WHERE b.bonus < 1000
+   OR b.bonus IS NULL;

ebelykh/postgresql/ПЭТ проект/Script.sql

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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;
+  
+  
+  

ebelykh/postgresql/агрегации и группировки/агрегации.sql

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+--Задача 1
+В варианте А: WHERE фильтрует товары и убирает те, которые не в наличии, потом эти товары(строки)участвуют в группировке, в варианте В - HAVING фильтрует уже сгруппированные данные(категории)
+
+--Задача 2356
+SELECT teacher_id,
+       COUNT(DISTINCT subject_id) AS cnt
+FROM teacher
+GROUP BY teacher_id;
+
+--Задача 1581
+SELECT customer_id,
+       COUNT(v.visit_id) AS count_no_trans
+FROM visits v
+LEFT JOIN transactions t
+ON v.visit_id = t.visit_id
+WHERE t.transaction_id IS NULL
+GROUP BY customer_id;
+
+--Задача 1141 
+SELECT activity_date AS day,
+       COUNT(DISTINCT user_id) AS active_users
+FROM Activity
+WHERE activity_date BETWEEN '2019-06-28' AND '2019-07-27'
+GROUP BY activity_date;
+
+--Задача 596
+SELECT class
+FROM Courses
+GROUP BY class
+HAVING COUNT(student) >= 5;
+
+--Задача 1075
+SELECT project_id,
+       ROUND(AVG(experience_years), 2) AS average_years
+FROM Project p
+JOIN Employee e
+ON p.employee_id = e.employee_id
+GROUP BY project_id;
+
+--Задача 1729
+SELECT user_id, 
+       COUNT (follower_id) AS followers_count 
+FROM followers 
+GROUP BY user_id
+ORDER BY user_id;
+
+--Задача 1633
+SELECT
+    r.contest_id,
+    ROUND(
+        COUNT(r.user_id) * 100.0 / (SELECT COUNT(*) FROM Users),
+        2
+    ) AS percentage
+FROM Register r
+GROUP BY r.contest_id
+ORDER BY percentage DESC, r.contest_id ASC;
+
+--Задача 1251
+SELECT
+    p.product_id,
+    COALESCE(
+        ROUND(
+             SUM(u.units * p.price) * 1.0 / NULLIF(SUM(u.units), 0),
+            2
+        ),
+        0
+    ) AS average_price
+FROM Prices p
+LEFT JOIN UnitsSold u
+    ON p.product_id = u.product_id
+    AND u.purchase_date BETWEEN p.start_date AND p.end_date
+GROUP BY p.product_id;

ebelykh/postgresql/базовый SQL/Select.sql

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+--Задача 1757
+SELECT product_id
+FROM Products
+WHERE low_fats = 'Y' AND recyclable = 'Y';
+
+--Задача 584
+SELECT name
+FROM Customer
+WHERE referee_id!= 2 OR referee_id IS NULL;
+
+--Задача 595
+SELECT name, population, area
+FROM World
+WHERE area >= 3000000
+   OR population >= 25000000;
+
+--Задача 1148 
+SELECT DISTINCT author_id AS id
+FROM Views
+WHERE author_id = viewer_id
+ORDER BY id; 
+
+--Задача 1683 
+SELECT tweet_id
+FROM Tweets
+WHERE CHAR_LENGTH(content) > 15;
+
+--Задача 620
+SELECT id, movie, description, rating
+FROM Cinema
+WHERE id % 2 = 1
+  AND description != 'boring'
+ORDER BY rating DESC;
+
+--Задача 1667
+SELECT
+  user_id,
+  CONCAT(
+    UPPER(SUBSTR(name, 1, 1)),
+    LOWER(SUBSTR(name, 2))
+  ) AS name
+FROM Users
+ORDER BY user_id;

ebelykh/postgresql/основы SQL/Script.sql

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+--Задача 1
+  CREATE TABLE products_extended (
+  id INT PRIMARY KEY,
+  name VARCHAR(100) NOT NULL,
+  category VARCHAR(50),
+  price DECIMAL(6,2),
+  in_stock BOOLEAN DEFAULT true,
+  email_support VARCHAR
+);
+
+
+--Задача 2 Вариант с DEFAULT (in_stock не указываем)
+INSERT INTO products_extended (id, name, category, price, email_support)
+VALUES
+(1, 'Mi Band 7', 'smartwatch', 49.00, 'miband@xiaomi.com'),
+(2, 'Surface Pro', 'tablet', 1299.00, 'surface@microsoft.com');
+
+--Задача 3
+ALTER TABLE products_extended  
+ADD COLUMN rating DECIMAL(3,2), 
+DROP COLUMN email_support;
+
+--Задача 4
+UPDATE products_extended
+SET price = price * 1.1
+WHERE name = 'Mi Band 7';
+
+--Задача 5(удаляет данные/таблицу)
+TRUNCATE TABLE products_extended;
+DROP TABLE products_extended;
+
+
+

ebelykh/postgresql/фильтрация/Script.sql

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+SELECT
+ name,
+ category,
+  price,
+  price * 1.10 AS price_with_markup,
+  price * 1.20 AS price_with_vat,
+  COALESCE(email_support, 'нет почты') AS status
+FROM products_extended
+WHERE in_stock = true
+  AND category NOT IN ('smartwatch', 'ebook_reader')
+  AND price BETWEEN 300 AND 1300;
+
+SELECT
+  name,
+  category,
+  email_support,
+  price * 1.25 AS price_25,
+  price > 1000 AS premium
+FROM products_extended
+WHERE (price < 150 OR price > 1200)
+  AND email_support IS NOT NULL;
+
+SELECT
+  id,
+  name,
+  category,
+  price
+FROM products_extended
+WHERE category IN ('smartphone', 'laptop', 'tablet')
+  AND name NOT LIKE '%i%'
+  AND price BETWEEN 500 AND 1300
+ORDER BY id;
+
+SELECT
+  name,
+  category,
+  price,
+  'нет поддержки' AS comment
+FROM products_extended
+WHERE in_stock = true
+  AND email_support IS NULL
+  AND price < 800;
+
+SELECT
+  name,
+  category,
+  price,
+  price > 1000 AS premium
+FROM products_extended
+WHERE (name LIKE '%Pro' OR name LIKE '%X%')
+  AND in_stock = true
+  AND price > 700;
+
+

ebelykh/postgresql/функции/функции.sql

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+--Задача 1211
+SELECT
+    query_name,
+    ROUND(AVG(rating * 1.0 / position), 2) AS quality,
+    ROUND(AVG(CASE WHEN rating < 3 THEN 1 ELSE 0 END) * 100,2) AS poor_query_percentage
+FROM Queries
+GROUP BY query_name;
+
+--Задача 1193
+SELECT
+    TO_CHAR(trans_date, 'YYYY-MM') AS month,
+    country,
+    COUNT(*) AS trans_count,
+    SUM(CASE WHEN state = 'approved' THEN 1 ELSE 0 END) AS approved_count,
+    SUM(amount) AS trans_total_amount,
+    SUM(CASE WHEN state = 'approved' THEN amount ELSE 0 END) AS approved_total_amount
+FROM Transactions
+GROUP BY
+    TO_CHAR(trans_date, 'YYYY-MM'),
+    country;