pmikhailov/postgresql/homework_window_functions.sql

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+/* Задание 1 */
+
+SELECT 
+	u.id,
+	u."name",
+	o.id AS order_id,
+	o.order_date,
+	ROW_NUMBER() OVER (
+		PARTITION BY u.id
+		ORDER BY o.order_date) AS order_number_for_user
+FROM 
+	users u 
+INNER JOIN
+	orders o ON u.id = o.user_id
+
+	
+/* Задание 2 */
+	
+WITH order_revenue_cte AS (
+	SELECT 
+		oi.order_id,
+		oi.quantity * oi.price_at_purchase AS order_revenue
+	FROM 
+		order_items oi
+	)
+SELECT 
+	u.id,
+	u."name",
+	o.id AS order_id,
+	o.order_date,
+	orc.order_revenue,
+	sum(orc.order_revenue) OVER (
+		PARTITION BY u.id
+		ORDER BY o.order_date 
+		ROWS UNBOUNDED PRECEDING
+	) AS running_revenue_for_user
+FROM 
+	users u 
+INNER JOIN
+	orders o ON u.id = o.user_id
+INNER JOIN 
+	order_revenue_cte orc ON o.id = orc.order_id
+	
+
+/* Задание 3 */
+	
+WITH user_revenue_cte AS (
+	SELECT 
+		o.user_id,
+		oi.quantity * oi.price_at_purchase AS order_revenue,
+		sum(oi.quantity * oi.price_at_purchase) OVER (
+			PARTITION BY o.user_id) AS user_total_revenue
+	FROM
+		orders o
+	INNER JOIN
+		order_items oi ON o.id = oi.order_id)
+SELECT DISTINCT
+	u."name",
+	urc.user_total_revenue,
+	RANK() OVER (ORDER BY urc.user_total_revenue DESC) AS revenue_rank,
+	DENSE_RANK() OVER (ORDER BY urc.user_total_revenue DESC) AS revenue_dense_rank
+FROM 
+	users u 
+INNER JOIN 
+	user_revenue_cte urc ON u.id = urc.user_id
+	
+
+/* Задание 4 */
+	
+SELECT 
+	u.name AS user_name,
+	o.id AS order_id,
+	o.order_date,
+	FIRST_VALUE(o.order_date) OVER (
+		PARTITION BY o.user_id
+		ORDER BY o.order_date
+	) AS first_order_date,
+	LAST_VALUE(o.order_date) OVER (
+		PARTITION BY o.user_id
+		ORDER BY o.order_date
+		ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
+	) AS last_order_date
+FROM 
+	users u 
+INNER JOIN
+	orders o ON u.id = o.user_id;
+	
+
+/* Задание 5 */
+
+SELECT 
+	u.name,
+	o.id,
+	count(o.id) OVER (
+		PARTITION BY o.user_id) AS orders_per_user 
+FROM
+	users u 
+INNER JOIN 
+	orders o ON u.id = o.user_id 
+
+
+/* Задание 6 */
+
+WITH order_revenue_cte AS (
+	SELECT 
+		oi.order_id,
+		oi.quantity * oi.price_at_purchase AS order_revenue
+	FROM 
+		order_items oi
+	)
+SELECT
+	u.name,
+	o.id,
+	o.order_date,
+	orc.order_revenue,
+	lag(orc.order_revenue) OVER (
+		PARTITION BY o.user_id
+		ORDER BY o.order_date
+	) AS prev_order_revenue
+FROM
+	users u 
+INNER JOIN
+	orders o ON u.id = o.user_id 
+INNER JOIN 
+	order_revenue_cte orc ON o.id = orc.order_id
+
+
+/* Задание 7 */
+
+WITH category_revenue_cte AS (
+	SELECT
+		p.category, 
+		date_trunc('day', o.order_date)::date AS order_period,
+		sum(oi.quantity * oi.price_at_purchase) AS daily_category_revenue
+	FROM
+		products p 
+	LEFT JOIN
+		order_items oi ON p.id = oi.product_id 
+	INNER JOIN 
+		orders o ON oi.order_id = o.id
+	GROUP BY 1, 2)
+SELECT 
+	cr_cte.*,
+	sum(cr_cte.daily_category_revenue) OVER (
+		PARTITION BY cr_cte.category
+		ORDER BY cr_cte.order_period
+		ROWS UNBOUNDED PRECEDING
+	) AS running_category_revenue
+FROM 
+	category_revenue_cte cr_cte;
+