mysql分组排序以及排序失效问题

一、要求

我们需要按公司分组，返回最新的一条消息，理论上

SELECT
	A.* 
FROM
	( SELECT * FROM `bac_distribution` ORDER BY distribution_id DESC ) A 
GROUP BY
	A.customer

就可以了吧，实际上查到的却是：

原因是mysql做了优化，直接将内查询去掉了。

EXPLAIN EXTENDED 
SELECT
	A.* 
FROM
	( SELECT DISTINCT * FROM `bac_distribution` ORDER BY distribution_id DESC ) A 
GROUP BY
	A.customer;
SHOW WARNINGS;

两行选中，一起查看

二、解决方案
在里面的查询上做一点操作就可以了 DISTINCT LINMIT都可以，倾向于第一个

SELECT A.* FROM
(SELECT DISTINCT* FROM `bac_distribution`  ORDER BY distribution_id desc ) A
GROUP BY A.customer

SELECT A.* FROM
(SELECT * FROM `bac_distribution`  ORDER BY distribution_id desc limit 10000) A
GROUP BY A.customer