两种实现方式

先 order by 之后再分组：

SELECT _ FROM (SELECT _ from tb_dept ORDER BY id descLIMIT 10000) a GROUP BY parent_id;

不加LIMIT可能会无效，由于 mysql 的版本问题。但是总觉得这种写法不太正经，因为如果数据量大于 Limit 的值后，结果就不准确了。所以就有了第二种写法。

SELECT * FROM tb_dept td,(SELECT max(id) id FROM tb_dept GROUP BY parent_id) md where td.id = md.id;

开发过程中真实 sql 语句举例：

1
select  * from (select * from guangnian_distribution order by id desc LIMIT 10000) m group by m.guangnian_id,m.user_id order by id desc