/* Задача 1
 * Джойним в таком порядке т.к. не каждый юзер делал заказ
 * + судя по порядку колонок мы хотим анализировать заказы
 * (по сути выглядит так же как INNER)
 * Но в обратном порядке можем увидеть кто не делал заказ
 * и добавить их в условную рассылку
 */
SELECT 
	o.id AS order_id, 
	o.order_date, 
	status, 
	u."name" AS user_name, 
	country
FROM 
	orders o
LEFT JOIN 
	users u ON o.user_id = u.id 
	

/* Задача 2 */
	
SELECT 
	order_id, 
	p."name" AS product_name, 
	quantity, 
	price_at_purchase
FROM 
	order_items oi
LEFT JOIN 
	products p ON oi.product_id = p.id  -- AND oi.order_id = 1 из правой таблицы будут NULL там, где оба условия не выполнены 
WHERE order_id = 1 -- в задании другой номер - 101, надо исправить в Notion, данные на п.4 уже другие


/* Задача 3 */

SELECT 
	order_id, 
	u."name" AS user_name,
	p."name" AS product_name, 
	quantity, 
	price_at_purchase
FROM
	orders o 
LEFT JOIN 
	order_items oi ON o.id =  oi.order_id 
INNER JOIN 
	users u ON o.id = u.id
INNER JOIN
	products p ON oi.product_id = p.id;


/* Задача 4 */

SELECT 
	u."name" AS user_name,
	o.id AS order_id,
	status
FROM 
	users u 
LEFT JOIN
	orders o ON u.id = o.user_id 


/* Задача 5 */

SELECT
	o.user_id,
	u."name" AS user_name
FROM
	users u 
LEFT JOIN
	orders o ON u.id = o.id
WHERE o.user_id IS NOT NULL


/* Задача 6 */

SELECT 
	o.id AS order_id,
	u.name AS user_name,
	p.name AS product_name,
	quantity
FROM
	orders o
LEFT JOIN
	order_items oi ON o.id = oi.order_id 
INNER JOIN 
	products p ON oi.product_id = p.id 
INNER JOIN 
	users u ON o.user_id = u.id
WHERE p."name" ILIKE '%Mi Band 7%';


/* Задача 7 */

SELECT 
	p.name AS product_name,
	order_id,
	quantity
FROM 
	products p 
FULL JOIN 
	order_items oi ON p.id = oi.product_id
ORDER BY product_name;


/* Задача 8 */

SELECT 
	o.id,
	u."name" AS user_name,
	p."name" AS product_name,
	quantity,
	price_at_purchase 
FROM 
	orders o 
LEFT JOIN 
	order_items oi ON o.id = oi.order_id 
INNER JOIN 
	users u ON o.user_id = u.id 
LEFT JOIN
	products p ON oi.product_id = p.id 
WHERE 
	o.status = 'paid';


/* Задача 9 */

SELECT 
	o.id AS order_id,
	o.order_date,
	p."name" AS product_name,
	quantity,
	price_at_purchase
FROM
	orders o
LEFT JOIN 
	order_items oi ON o.id = oi.order_id
INNER JOIN 
	products p ON oi.product_id = p.id 
INNER JOIN 
	users u ON o.user_id = u.id
WHERE u."name" ILIKE '%alice%';


/* Задача 10 
* Задача противоречит изначальным органичениям NOT NULL
*/

SELECT 
	o.id AS order_id,
	user_id,
	status
FROM
	orders o 
FULL JOIN
	order_items oi ON oi.order_id = o.id 
WHERE product_id IS NULL AND o.status = 'created';