求一条简单的语句！！
table1表(字段a1,字段a2,字段a3)
求一条语句，得到下面的结果集：

N SUM
-----------------
N1 sum(a1)
N2 sum(a2)
N3 sum(a3)

//N1，N2，N3为任意标识

即得到上面三条数据，求解！

[解决办法]
这样:

select 'N1' as N,sum(a1) as [SUM] from table1
union all
select 'N2',sum(a2) from table1
union all
select 'N3',sum(a3) from table1

[解决办法]
这不是就三条数据吗？
select 'N1',sum(a1) from table1
union all
select 'N2',sum(a2) from table1
union all
select 'N3',sum(a3) from table1

[解决办法]
union 常规防范，求高手帮顶