求mysql一条语句,该如何处理

求mysql一条语句
按id降序查询几种情况的各一条记录，用一条语句能否实现？

------解决方案--------------------
union 可不可以的，没用过
------解决方案--------------------
对

(select * from a order by id desc limit 0,1) union all (select * from b order by id desc order by id desc limit 0,1)
------解决方案--------------------
可以啊，用UNION ALL
------解决方案--------------------
按情况分组 每组取一条记录

SQL code

SELECT * FROM (SELECT * FROM `table` ORDER BY `condition` DESC) t GROUP BY `condition`; <div class="clear"></div>