sql-server-2008 - 如何获得具有不同别名的两个表的联合

Question

我想得到联合，但想用不同的别名显示一列两次。例如

Select a as first from table1 
union 
select a as second from table1

它首先显示为输出。

但我想同时展示第一和第二。在 MSSQL 中如何实现？

Answer 1

Union 将两个查询的结果合并到一组列中。没有办法让列名更改一半。我能想到的最接近的是

select a as first
, null as second 
from table1 

union all 

select null as first
, a as second 
from table1

Answer 2

您将拥有所有行union all

Select a as first from table1 
union all 
select a as second from table1

Answer 3

如果我做对了：

Select a as first,a as second from table1