MySQL删除重复数据行，只保存一条

delimiter $$

CREATE TABLE `devices_all` (
 `device_all_id` int(11) NOT NULL AUTO_INCREMENT,
 `device_id` varchar(512) DEFAULT NULL,
 `device_token` varchar(512) DEFAULT NULL,
 `client_agent` varchar(512) DEFAULT NULL,
 `create_time` datetime DEFAULT NULL,
 PRIMARY KEY (`device_all_id`)
) ENGINE=MyISAM AUTO_INCREMENT=49 DEFAULT CHARSET=latin1$$

delete from devices_all
where device_id in (select device_id from (select device_id from devices_all a group by a.device_id having count(a.device_id) > 1) as a) 
and device_all_id not in (select device_all_id from (select min( device_all_id) device_all_id from devices_all group by device_id having count( device_id)>1) as b)