10. (15 points) Suppose you work in one of the MIS department of the above supermaket. The marketing team proposes some promotion strategies to increase the sales. The team may propose the promotion, like 兩件合購(如飯糰 + 咖啡)39元、第二罐6折、刷悠遊卡買便當少10元、可樂買一送一、超過1000元送Hello kitty 一隻、… Suppose each item can be discounted only once, not allowing more than one discount upon the same item. Thus, the IT department asks the management department can not set the promotion strategy such that one item can involve only one promotion. Please design the tables, which support/record the promotion strategies and the trigger to re-compute the price and remind the clerk if the buying satisfies the condition of the promotion.