MySQL从2个或更多列中删除所有唯一值

我试图从一个非统一的表中选择唯一的值,并且只显示唯一的值。

SELECT DISTINCT "year" as sorter, year(data) as year, NULL as location
FROM site 
WHERE tipo='projects'

UNION

SELECT DISTINCT "loc" as sorter, NULL as year, spare_1 as location
FROM site 
WHERE tipo='projects'

ORDER BY sorter ASC, year DESC, localition ASC

这会回来的

+--------+------+----------+
| SORTER | YEAR | LOCATION |
+--------+------+----------+
| year   | 2010 | NULL     |
+--------------------------+
| year   | 2009 | NULL     |
+--------------------------+
| year   | 2008 | NULL     |
+--------------------------+
| loc    | NULL | London   |
+--------------------------+
| loc    | NULL | Paris    |
+--------------------------+
| loc    | NULL | NYC      |
+--------------------------+

我真的不喜欢双选。有没有比这更有效的方法?

先谢谢你。