mysql "group by"与"order by"的研究－－分类中最新的内容

代码如下：

CREATE TABLE `test` ( 
`id` INT(10) NOT NULL AUTO_INCREMENT, 
`name` VARCHAR(255) NOT NULL, 
`category_id` INT(10) NOT NULL, 
`date` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP, 
PRIMARY KEY (`id`) 
) 
ENGINE=MyISAM 
ROW_FORMAT=DEFAULT; 
INSERT INTO `test` (`id`, `name`, `category_id`, `date`) 
VALUES 
(1, 'aaa', 1, '2010-06-10 19:14:37'), 
(2, 'bbb', 2, '2010-06-10 19:14:55'), 
(3, 'ccc', 1, '2010-06-10 19:16:02'), 
(4, 'ddd', 1, '2010-06-10 19:16:15'), 
(5, 'eee', 2, '2010-06-10 19:16:35');

select * from test group by category_id order by `date`