All homework SQL2.0 done in one file

2026-02-15 15:30:39 +03:00
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+-----------------------------------------------------------
+--DDL
+create table users (
+id INT primary key not null,
+name VARCHAR(100),
+age INT,
+email VARCHAR(100),
+country VARCHAR(50),
+is_active BOOLEAN,
+created_at DATE
+);
+
+create table products (
+id INT primary key,
+name VARCHAR(100) not null,
+category VARCHAR(50),
+price DECIMAL(10, 2) not null,
+in_stock BOOLEAN
+);
+
+create table orders (
+id INT primary key,
+user_id INT,
+order_date DATE not null,
+status VARCHAR(20)
+);
+
+create table order_items (
+order_id INT,
+product_id INT,
+quantity INT not null,
+price_at_purchase DECIMAL(10, 2) not null,
+primary key (order_id, product_id)
+);
+
+alter table users
+alter column created_at type timestamptz;
+
+--------------------------------------------------------------------------------------
+-- DML
+INSERT INTO users (id, name, age, email, country, is_active, created_at) 
+VALUES
+(1, 'Alice', 25, 'alice@example.com', 'US', true, '2024-01-10 10:00:00'),
+(2, 'Bob', 30, 'bob@example.com', 'UK', true, '2024-02-05 09:30:00'),
+(3, 'Carol', 27, 'carol@example.com', 'US', false, '2024-03-01 15:20:00'),
+(4, 'Diana', 22, 'diana@GMAIL.com', 'US', true, '2024-01-12 08:15:00'),
+(5, 'Evan', 35, 'EVAN@example.com', 'UK', true, '2024-01-18 19:40:00'),
+(6, 'Farida', 29, 'farida@example.com', 'KZ', true, '2024-02-20 11:05:00'),
+(7, 'George', 31, 'george+test@example.com', 'US', true, '2024-03-05 16:45:00'),
+(8, 'Helen', 24, NULL, 'UK', false, '2024-03-06 08:20:00'),
+(9, 'Ivan', 26, 'ivan@example.com', 'RU', true, '2024-01-11 14:30:00'),
+(10, 'Julia', 28, 'julia@example.com', 'US', true, '2024-03-07 18:05:00');
+
+
+INSERT INTO products (id, name, category, price, in_stock) 
+VALUES
+(1, 'iPhone 15', 'Электроника', 80000, true),
+(2, 'Kindle', 'Электроника', 15000, true),
+(3, 'Кроссовки Nike', 'Одежда', 9000, true),
+(4, 'Кроссовки NoName', 'Одежда', 3000, false),
+(5, 'Наушники Pro', 'Электроника', 12000, true),
+(6, 'Фитнес‑браслет', 'Гаджеты', 6000, true),
+(7, 'Подарочная карта', 'Сервисы', 1000, true);
+
+
+INSERT INTO orders (id, user_id, order_date, status) 
+VALUES
+(1, 1, '2025-01-10 12:00:00', 'paid'),
+(2, 3, '2025-01-12 09:30:00', 'cancelled'),
+(3, 1, '2025-01-15 18:20:00', 'paid'),
+(4, 2, '2025-01-20 11:05:00', 'created'),
+(5, 4, '2025-02-01 17:45:00', 'paid'),
+(6, 5, '2025-02-10 10:10:00', 'refunded'),
+(7, 7, '2025-03-01 09:00:00', 'paid'),
+(8, 9, '2025-03-05 19:30:00', 'paid');
+
+
+INSERT INTO order_items (order_id, product_id, quantity, price_at_purchase) 
+VALUES
+(1, 1, 1, 78000),
+(1, 3, 2, 8500),
+(2, 2, 1, 14000),
+(3, 5, 1, 11000),
+(3, 7, 1, 1000),
+(4, 2, 1, 15000),
+(5, 6, 1, 6000),
+(6, 1, 1, 82000),
+(7, 3, 1, 9000),
+(8, 4, 2, 2800);
+
+
+--------------------------------------------------------------------------------------------
+--BASE SQL
+select id, name, country, created_at, email from users
+order by created_at desc, name;
+
+select id, name, country from users
+where country = 'US' -- 'UK'
+order by name;
+
+select id, name, email from users
+where email is not null
+order by name;
+
+select distinct LOWER(email) as email_lower from users
+where email is not null;
+
+select id, name, created_at from users
+where created_at > '2024-01-11'
+order by created_at desc
+limit 2 offset 1;
+------------------------------------------------------------------------------------------------------
+-- FILTRATION
+select name, category, price, 
+price * 1.3 as price_with_markup, 
+price * 1.5 as price_with_vat from products
+where in_stock is true 
+and category not in ('Гаджеты')
+and price >= 100 and price <=1300;
+
+select name, price,
+price * 0.85 as price_with_discount
+from products
+where price < 100 or price > 1000;
+
+select id, name, category, price from products
+where category in ('Электроника') and price >= 15000;
+
+select name, category, price from products
+where name not like '%iPhone%';
+
+select * from products
+where name ilike '%pro%';
+
+---------------------------------------------------------------------------------------------------
+-- JOIN
+-- 1 задание
+select o.id as order_id, order_date, status, u.name as user_name, country from orders o
+join users u on o.user_id = u.id;
+
+-- 2 задание
+
+select o.id as order_id, p.name as product_name, oi.quantity, oi.price_at_purchase from orders o
+join order_items oi on o.id = oi.order_id
+join products p on oi.product_id = p.id
+where o.id = 1;
+
+-- 3 задание
+select o.id as order_id, p.name as product_name, oi.quantity, oi.price_at_purchase from orders o
+join order_items oi on o.id = oi.order_id
+join products p on oi.product_id = p.id;
+
+-- 4 задание
+select u.name as user_name, o.id as order_id, o.status from users u
+left join orders o on u.id = o.user_id;
+
+-- 5 задание
+select u.id as user_id, u.name as user_name from users u
+left join orders o on u.id = o.user_id
+where o.user_id is null;
+
+-- 6 задание
+
+select o.id as order_id, p.name as product_name, oi.quantity, oi.price_at_purchase from orders o
+join order_items oi on o.id = oi.order_id
+join products p on oi.product_id = p.id
+where p.name = 'Фитнес‑браслет';
+
+-- 7 задание
+
+select o.id as order_id, p.name as product_name, oi.quantity, oi.price_at_purchase from orders o
+join order_items oi on o.id = oi.order_id
+join products p on oi.product_id = p.id
+where o.status = 'paid';
+
+-- 8 задание
+
+select o.id, o.order_date, p.name as product_name, oi.quantity, oi.price_at_purchase from orders o
+join order_items oi on o.id = oi.order_id
+join products p on oi.product_id = p.id
+where o.user_id in (select id from users where name = 'Alice');
+
+-- 9 задание
+
+select o.id as order_id, o.user_id, o.status from orders o
+left join order_items oi on o.id = oi.order_id
+where oi.product_id is null; -- таких у нас заказов нет, во всех заказах есть товары.
+
+--------------------------------------------------------------------------------------------
+-- UNION
+-- 1 задание
+select id, name, is_active from users
+where is_active is false
+union
+select id, name, is_active from users
+where is_active is true
+order by name;
+
+-- 2 задание
+select id as order_id, user_id, order_date, 
+case when o.order_date < '2025-02-01' then 'old' else 'new' end as period
+from orders o;
+-- 3е задание не имеет смысла, т.к. все заказы покупались, там нечего соединять
+
+----------------------------------------------------------------------------------------------
+-- Agregation
+-- 1 задание
+select category, COUNT(*) as products_count from products
+group by category
+order by products_count desc;
+
+-- 2 задание
+select order_id, SUM(quantity) as total_quantity, SUM(quantity * price_at_purchase) as order_revenue from order_items
+group by order_id
+order by order_revenue desc;
+
+-- 3 задание
+select p.category, SUM(oi.quantity * oi.price_at_purchase) as category_revenue from products p 
+join order_items oi on oi.product_id = p.id
+group by p.category
+order by category_revenue desc;
+
+-- 4 задание
+select order_id, SUM(quantity * price_at_purchase) as order_revenue from order_items oi
+join orders o on oi.order_id = o.id
+where o.status = 'paid'
+group by oi.order_id
+order by order_revenue desc;
+
+-- 5 задание
+select p.category, SUM(oi.quantity * oi.price_at_purchase) as category_revenue from products p 
+join order_items oi on oi.product_id = p.id
+group by p.category
+having SUM(oi.quantity * oi.price_at_purchase) > 1000
+order by category_revenue desc;
+
+-- 6 задание
+select country, COUNT(*) as active_users_count 
+from users
+where is_active is true
+group by country
+having COUNT(*) >= 2
+order by active_users_count desc;
+
+-- 7 задание
+select p.name, SUM(oi.quantity) as total_quantity_sold from products p
+join order_items oi on oi.product_id = p.id
+group by p.name
+order by total_quantity_sold desc
+limit 3;
+
+-- 8 задание
+
+select order_id, SUM(quantity * price_at_purchase) as order_revenue 
+from order_items
+group by order_id
+having SUM(quantity * price_at_purchase) < 10000 -- сделал меньше 10000 потому что заказов дешевле 100 нет.
+order by order_revenue;
+
+--------------------------------------------------------------------------------------------------------------
+--Functions:date strings logic
+-- 1 задание
+select name, 
+created_at::date as created_date,
+CURRENT_DATE - created_at::date as days_since_registration
+from users
+where CURRENT_DATE - created_at::date > 750
+order by days_since_registration desc;
+
+-- 2 задание
+select name, LOWER(email) as email_clean, 
+substring(LOWER(email) from position('@' in email) + 1) as domain 
+from users
+where email is not null
+order by domain, name;
+
+-- 3 задание
+select name, age,
+case when age < 25 then 'young'
+	 when age between 20 and 30 then 'adult'
+	 else 'senior'
+	 end as age_group
+from users 
+order by age;
+
+-- 4 задание
+with CTE as 
+		(select name, created_at::date,
+		current_date - created_at::date as days_since_registration,
+		case when is_active = true then 'hot'
+			 when current_date - created_at::date < 30 then 'hot'
+			 else 'regular'
+			 end as hot_flag
+		from users)
+select * from CTE
+where hot_flag = 'hot';
+
+-- 5 задание
+with CTE as 
+		(select count(id) as total_users,
+		COUNT(email) as with_email,
+		(select count(*) from users where email is null) as without_email
+		from users)
+select total_users, with_email, without_email,
+ ROUND(100.0 * without_email / total_users, 2) as percentage_no_email
+ from CTE;
+ 
+ -- 6 задание
+ select name, 
+ CURRENT_DATE - created_at::date as days_since_registration,
+ case
+ 	when CURRENT_DATE - created_at::date <= 720 then 'new'
+ 	when CURRENT_DATE - created_at::date BETWEEN 721 and 750 then 'middle'
+ 	else 'old'
+ 	end as tenure_group
+ from users
+ order by days_since_registration;
+ 
+ ----------------------------------------------------------------------------------------------------
+ --Subquery/CTE
+ -- 1 задание
+select name 
+from users
+where id in (select distinct user_id from orders)
+order by name;
+
+-- 2 задание
+select id, name, email 
+from users u
+where not exists (
+select user_id 
+from orders o
+where o.user_id = u.id)
+
+-- 3 задание
+select name, 
+(select COUNT(*) orders_count from orders o 
+where o.user_id = u.id)
+from users u
+order by orders_count desc, name;
+
+-- 4 задание
+with CTE as (
+			select user_id, SUM(quantity * price_at_purchase) as total_revenue
+			from orders o
+			join order_items oi on o.id = oi.order_id
+			group by user_id
+			)
+select u.name, c.total_revenue from users u
+join CTE c on u.id = c.user_id
+order by c.total_revenue desc;
+
+-- 5 задание
+with CTE as (
+			select product_id, SUM(quantity * price_at_purchase) as product_revenue 
+			from order_items
+			group by product_id
+			)
+select p.name as product_name, p.category, c.product_revenue from CTE c
+join products p on c.product_id = p.id
+order by c.product_revenue desc
+limit 3;
+
+-- 6 задание
+with CTE as (
+			select o.user_id, SUM(quantity * price_at_purchase) as total_revenue from orders o 
+			join order_items oi on o.id = oi.order_id
+			group by o.user_id
+			)
+select u.name, u.email, c.total_revenue from users u
+join CTE c on u.id = c.user_id
+where u.is_active is true 
+and c.total_revenue > 10000;
+
+-- 7 задание
+
+with CTE as (
+			select order_id, SUM(quantity * price_at_purchase) as order_revenue 
+			from order_items oi
+			join orders o on oi.order_id = o.id
+			where o.status = 'paid'
+			group by order_id
+			)
+select * from CTE
+where order_revenue < 10000;
+			
+---------------------------------------------------------------------------------------------
+--WINDOW FUNCTIONS
+-- 1 задание
+select u.id as user_id, u.name, o.id as order_id, o.order_date,
+row_number() over (partition by o.user_id order by o.order_date) as order_number_for_user
+from users u
+join orders o on u.id = o.user_id;
+
+-- 2 задание
+with CTE as (
+			select u.id as user_id, u.name as user_name, order_id, o.order_date, SUM(quantity * price_at_purchase) as order_revenue
+			from order_items oi
+			join orders o on oi.order_id = o.id
+			join users u on o.user_id = u.id
+			group by u.id, u.name, order_id, o.order_date
+			order by user_id
+			)
+select user_id, user_name, order_id, order_date, order_revenue,
+SUM(order_revenue) over (partition by user_id order by order_date) as running_revenue_for_user
+from CTE
+
+-- 3 задание
+with CTE as (
+			select u.id as user_id, u.name as user_name, SUM(quantity * price_at_purchase) as total_revenue
+			from order_items oi
+			join orders o on oi.order_id = o.id
+			join users u on o.user_id = u.id
+			group by u.id, u.name
+			)
+select user_name, total_revenue,
+RANK() over (order by total_revenue desc) as revenue_rank,
+dense_rank() over (order by total_revenue desc) as dense_revenue_rank
+from CTE;
+
+
+-- 4 задание
+select u.name, o.id as order_id, order_date, 
+first_value(o.order_date) over (partition by user_id order by order_date) as first_order_date,
+last_value(o.order_date) over (partition by user_id order by order_date ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) as last_order_date
+from orders	o
+join users u on u.id = o.user_id;
+
+
+-- 5 задание
+select u.name as user_name, o.id as order_id,
+COUNT(*) over (partition by u.id) as orders_per_user
+from users u
+join orders o on u.id = o.user_id;
+
+-- 6 задание
+with CTE as (
+			select u.id as user_id, u.name as user_name, order_id, o.order_date as order_date, 
+			SUM(quantity * price_at_purchase) as order_revenue
+			from order_items oi
+			join orders o on oi.order_id = o.id
+			join users u on o.user_id = u.id
+			group by u.id, u.name, order_id, o.order_date
+			order by user_id
+			)
+select user_name, order_id, order_date, order_revenue,
+LAG(order_revenue) over (partition by user_id order by order_date) as prev_order_revenue
+from CTE;
+
+-- 7 задание
+with CTEa as (
+			select product_id, 
+			o.order_date::date as order_date, 
+			SUM(quantity * price_at_purchase) as daily_category_revenue
+			from order_items oi
+			join orders o on oi.order_id = o.id
+			group by product_id, order_date
+			order by oi.product_id
+			),
+	CTEb as (
+	select p.category, order_date, daily_category_revenue
+	from CTEa a
+	join products p on a.product_id = p.id
+	)
+select category, order_date, daily_category_revenue,
+SUM(daily_category_revenue) over (partition by category order by order_date) as running_category_revenue
+from CTEb;
+
+-----------------------------------------------------------------------------------------------------------				
+-- VIEW and MATERIALIZED VIEW
+-- 1 задание
+create MATERIALIZED view mv_category_revenue 
+as 
+	select p.category, SUM(quantity * price_at_purchase) as total_revenue
+	from products p
+	join order_items oi on oi.product_id = p.id
+	join orders o on oi.order_id = o.id and o.status = 'paid'
+	group by p.category
+	order by total_revenue desc
+;
+
+-- 2 задание
+create materialized view 
+as
+	select u.id, u.name, COUNT(o.id) as order_count 
+	from users u
+	join orders o on u.id = o.user_id and o.status = 'paid'
+	group by u.id, u.name
+	order by order_count desc
+;
+
+-- 3 задание
+create materialized view mv_daily_revenue
+as 
+	select order_date::date as sales_date, SUM(quantity * price_at_purchase) as daily_revenue from orders o
+	join order_items oi on o.id = oi.order_id
+	where o.status = 'paid'
+	group by sales_date
+	order by sales_date
+;
+
+-- 4 задание
+refresh materialized view mv_daily_revenue;
+
+-- В 1 случае витрину можно обновлять 1 раз в день в 10:00 или 2 раза в день в 10:00 и в 22:00
+-- Во 2 случае витрину нужно обновлять несколько раз в день, думаю каждые часа 2-3 то есть в 8 в 10 в 12 и тд.
+						
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