相关疑难解决方法(0)

以下查询在几乎每个数据库(提供或获取虚拟表)中都非常有效dual,包括Oracle:

select 'A' as x from dual union all
select 'B'      from dual
order by x asc

返回:

| X |
|---|
| A |
| B |

现在这个查询仍然是非常标准的SQL,但不适用于Oracle

select 'A' as x from dual union all
select 'B'      from dual union all
select 'C'      from dual
order by x asc

我越来越

ORA-00904: "X": invalid identifier

但是,这有效:

select 'A' as x from dual union all
select 'B' as x from dual union all …