例1：
SELECT 1 order2 FROM dual
union all
SELECT 3 order2 FROM dual
union all
SELECT 2 order1 FROM dual
order by 1
order by 是针对整个集合的排队，order by 1 表示第一列排序。
例1：
SELECT 1 order2 FROM dualunion all
SELECT 3 order2 FROM dual
union all
SELECT 2 order2 FROM dual
order by order2
或者把列名都起一样的名字。order by order2 表示第一列排序。