行程和用户。以下为输出结果，请问sql语句如何写？
±-----------±------------------+
| Day | Cancellation Rate |
±-----------±------------------+
| 2013-10-01 | 0.33 |
| 2013-10-02 | 0.00 |
| 2013-10-03 | 0.50 |
±-----------±------------------+

DROP TABLE IF EXISTS `trips`;
CREATE TABLE `trips` (
  `id` int(11) NOT NULL,
  `client_id` int(11) NOT NULL,
  `driver_id` int(11) NOT NULL,
  `city_id` int(11) NOT NULL,
  `status` enum('cancelled_by_client','cancelled_by_driver','completed') NOT NULL,
  `request_at` date NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
INSERT INTO `trips` VALUES ('1', '1', '10', '1', 'completed', '2013-10-01');
INSERT INTO `trips` VALUES ('2', '2', '11', '1', 'cancelled_by_driver', '2013-10-01');
INSERT INTO `trips` VALUES ('3', '3', '12', '6', 'completed', '2013-10-01');
INSERT INTO `trips` VALUES ('4', '4', '13', '6', 'cancelled_by_client', '2013-10-01');
INSERT INTO `trips` VALUES ('5', '1', '10', '1', 'completed', '2013-10-02');
INSERT INTO `trips` VALUES ('6', '2', '11', '6', 'completed', '2013-10-02');
INSERT INTO `trips` VALUES ('7', '3', '12', '6', 'completed', '2013-10-02');
INSERT INTO `trips` VALUES ('8', '2', '12', '12', 'completed', '2013-10-03');
INSERT INTO `trips` VALUES ('9', '3', '10', '12', 'completed', '2013-10-03');
INSERT INTO `trips` VALUES ('10', '4', '13', '12', 'cancelled_by_driver', '2013-10-03');

DROP TABLE IF EXISTS `users`;
CREATE TABLE `users` (
  `users_id` int(11) NOT NULL,
  `banned` enum('No','Yes') NOT NULL,
  `role` enum('partner','driver','client') NOT NULL,
  PRIMARY KEY (`users_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

INSERT INTO `users` VALUES ('1', 'No', 'client');
INSERT INTO `users` VALUES ('2', 'Yes', 'client');
INSERT INTO `users` VALUES ('3', 'No', 'client');
INSERT INTO `users` VALUES ('4', 'No', 'client');
INSERT INTO `users` VALUES ('10', 'No', 'driver');
INSERT INTO `users` VALUES ('11', 'No', 'driver');
INSERT INTO `users` VALUES ('12', 'No', 'driver');
INSERT INTO `users` VALUES ('13', 'No', 'driver');

sql语句如下：

SELECT T.request_at AS `Day`, 
	ROUND(
			SUM(
				IF(T.STATUS = 'completed',0,1)
			)
			/ 
			COUNT(T.STATUS),
			2
	) AS `Cancellation Rate`
FROM trips AS T
WHERE 
T.Client_Id NOT IN (
	SELECT users_id
	FROM users
	WHERE banned = 'Yes'
)
AND
T.Driver_Id NOT IN (
	SELECT users_id
	FROM users
	WHERE banned = 'Yes'
)
AND T.request_at BETWEEN '2013-10-01' AND '2013-10-03'
GROUP BY T.request_at