ORDER BY

按日期排序

SELECT
	*
FROM
	e_eledata AS a
ORDER BY
	a.DLDT DESC

参考：http://www.cnblogs.com/zsphper/archive/2010/06/10/mysql-group-by-order-by.html  

这个文章里提到了如何让  排序order by和 分组（group by）同时使用

排序并去除重复

排序用group by

去除重复用max(expr)

SELECT ed.ID,ed.`NAME`,ed.RATIO,max(e.DLDT),e.TAE,e.TAE/ed.RATIO 
from e_eledata e , e_elemeterhead ed 
where e.E_ELEMETERHEAD_ID = ed.ID  
and ed.`STATUS` = '0'
group by ed.ID,ed.`NAME`,ed.RATIO	;