更新 '2207/习题答案/2-18.md'

2207/习题答案/2-18.md

@@ -62,4 +62,65 @@ void main()
 	printf("%d\n",i);
 }
 
+```
+
+## MySQL
+
+```sql
+#1
+ALTER TABLE t_hotel ADD `level` CHAR(10) DEFAULT '暂无评级';
+#2
+INSERT INTO t_hotel()
+VALUES(DEFAULT, '苹果酒店', '无名街356号', '138-1258-0000', '五星');
+#3
+UPDATE t_room r
+SET r.price = r.price+100
+WHERE r.hid = (
+	SELECT hid
+	FROM t_hotel
+	WHERE hname = '香蕉酒店'
+);
+#4
+SELECT c.cname, c.integral, 
+IF(c.integral<1000, '普通会员', 
+IF(c.integral<3000, '中级会员', 
+IF(c.integral<5000, '高级会员', '顶级会员')))
+FROM t_client c;
+#5
+SELECT h.hid, ROUND(AVG(r.price), 2) p
+FROM t_hotel h, t_room r
+WHERE h.hid = r.hid
+GROUP BY h.hid
+ORDER BY p DESC;
+#6
+SELECT c.cid, c.cname, SUM(r.price) s
+FROM t_client c, t_booking b, t_room r
+WHERE c.cid = b.cid AND r.rid = b.rid
+GROUP BY c.cid
+ORDER BY s DESC
+LIMIT 1;
+#7
+CREATE VIEW v_hotel AS
+SELECT DATE_FORMAT(b.btime,'%Y-%m') d, SUM(r.price)
+FROM t_booking b, t_room r
+WHERE b.rid = r.rid
+GROUP BY d;
+#8
+DELIMITER $$
+CREATE TRIGGER tri_updateLevel
+BEFORE UPDATE ON t_client
+FOR EACH ROW
+BEGIN
+	IF NEW.integral <2500 THEN
+		SET NEW.`level` = '初级会员';
+	ELSEIF NEW.integral <5000 THEN
+		SET NEW.`level` = '中级会员';
+	ELSE
+		SET NEW.`level` = '高级会员';
+	END IF;
+END $$
+DELIMITER ;
+#9
+
+
 ```