MySQL如何查询两列互不重复的记录？

Question

数据如下：

id     date         fromId      toId
--------------------------------------
 1     2013-01-01     1           2
 2     2013-01-02     2           1
 3     2013-01-03     1           3
 4     2013-01-04     3           1
 5     2013-01-05     4           1
 6     2013-01-06     1           4

如何才能查询出fromId或toId包含某个值，但fromId和toId不相互重复的数据？ 例如，查询fromId或toId包含1，去除fromId和toId中数据互换的列，仅取日期最大的值，查询结果为：

 id     date         fromId      toId
--------------------------------------
 2     2013-01-02     2           1
 4     2013-01-04     3           1
 6     2013-01-06     1           4

Answer 1

SELECT max(`date`),maxId,minId FROM (SELECT `date`,IF(fromId>toId,fromId,toId) AS maxId,IF(fromId>toId,toId,fromId) AS minId FROM `table`) AS `tmp` GROUP BY maxId,minId

Answer 2

select distinct fromId,* from table group by toId;