1、select kd.CREATEUSERID as userid,kd.LOCATION,kd.createtime as location from KT_DEVICESTRACK kd where rownum=1 order by kd.createtime
2、SELECT * FROM ( SELECT *,ROWNUM rn FROM t ORDER BY date_col DESC ) WHERE rn = 1
原文：http://www.cnblogs.com/xinxin1994/p/6516528.html