/* #8 */
SELECT c.name, pro.name, sa.price, sa.quantity, sa.sell_date FROM customer c
JOIN sales sa JOIN sales_stock ss JOIN stock st JOIN product pro
WHERE sell_date >= GETDATE() - 31

/* #9 */
SELECT * FROM stock WHERE quantity < 10;

/* #10 */
SELECT * from stock WHERE entry_date < GETDATE() - 365
DELETE * from stock WHERE entry_date < GETDATE() - 365