homework "6) Агрегации и группировки" done

pmikhailov/postgresql/homework-aggregation-groupby.sql

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+/* Задание 1 */
+
+SELECT 
+	category,
+	count(*) AS products_count 
+FROM 
+	products p
+GROUP BY category 
+ORDER BY products_count DESC;
+
+
+/* Задание 2
+ * Тут всё решение в задании 
+ *  */
+
+SELECT 
+	order_id,
+	sum(quantity) AS total_quantity,
+	sum(quantity * price_at_purchase) AS order_revenue
+FROM 
+	order_items oi 
+GROUP BY order_id 
+ORDER BY order_revenue DESC;
+
+
+/* Задание 3 */
+
+SELECT 
+	p.category,
+	COALESCE(sum(oi.quantity * oi.price_at_purchase), 0) AS category_revenue
+FROM
+	products p
+LEFT JOIN
+	order_items oi ON p.id = oi.product_id 
+GROUP BY p.category 
+
+
+/* Задание 4 */
+
+SELECT 
+	o.id AS order_id,
+	sum(oi.quantity * oi.price_at_purchase) AS order_revenue 
+FROM
+	orders o 
+LEFT JOIN
+	order_items oi ON o.id = oi.order_id  
+WHERE o.status = 'paid'
+GROUP BY 1
+ORDER BY 2 DESC 
+
+
+/* Задание 5 */
+
+SELECT 
+	p.category,
+	COALESCE(sum(oi.quantity * oi.price_at_purchase), 0) AS category_revenue
+FROM
+	products p
+LEFT JOIN
+	order_items oi ON p.id = oi.product_id 
+GROUP BY 
+	p.category 
+HAVING  
+	sum(oi.quantity * oi.price_at_purchase) > 1;
+
+
+/* Задание 6 */
+
+SELECT 
+	country,
+	count(is_active) AS active_users_count 
+FROM 
+	users u 
+WHERE
+	is_active = TRUE 
+GROUP BY 
+	country
+HAVING 
+	count(is_active) > 2;
+
+
+/* Задание 7 */
+
+SELECT 
+	p.name AS product_name,
+	COALESCE (sum(oi.quantity), 0) AS total_quantity_sold 
+FROM
+	products p 
+LEFT JOIN
+	order_items oi ON p.id = oi.product_id 
+GROUP BY p.name
+ORDER BY 2 DESC 
+LIMIT 3
+
+
+/* Задание 8 
+ * Условие для HAVING в задаче кривое, < 100 ничего нет
+ * */
+
+SELECT 
+	order_id,
+	SUM(quantity * price_at_purchase) AS order_revenue 
+FROM	
+	order_items oi 
+GROUP BY
+	order_id
+HAVING 
+	SUM(quantity * price_at_purchase) < 10000
+ORDER BY 2;
+
+