编写一个SQL查询以显示订单号，购买金额，已实现的订单，以及那些超过目标值6000的50％的订单的未实现百分比。

数据库项目说明
mysql>describe orders;
FieldTypeNullKeyDefaultExtra
ord_no int(11) NO PRI NULL
purch_amt int(11) NO NULL
ord_date date NO NO
customer_id int(11) YES NULL
salesman_id int(11) NO NULL
5 rows in set (0.01 sec)

insert into orders values 
(70008, 5760, "2012-09-10", 3002, 5001),
(70010, 1983.43, "2012-10-10", 3004, 5006),
(70003, 2480.4, "2012-10-10", 3009, 5003),
(70012, 250.45, "2012-06-27", 3008, 5002),
(70011, 75.29, "2012-08-17", 3003, 5007),
(70013, 3045.6, "2012-04-25", 3002, 5001);

我这里把6000作为门槛，不足6000的百分比0

SELECT ord_no, purch_amt,
  CASE WHEN purch_amt >= 6000 THEN '已实现' ELSE '未实现' END AS order_status,
  CASE WHEN purch_amt >= 6000 AND purch_amt < 12000 THEN 100 - ((purch_amt - 6000) / 6000 * 100) ELSE 0 END AS unrealized_percentage
FROM orders;