Oracle UNION和ORDER BY的奇怪问题
Oracle UNION和ORDER BY的奇怪问题
提问于 2014-08-19 23:58:38
下面的查询在几乎每个数据库(或多或少一个dual虚拟表)中都是perfectly valid的，包括Oracle：
select 'A' as x from dual union all
select 'B' from dual
order by x asc正在返回：
| X |
|---|
| A |
| B |现在，这个查询仍然是非常标准的SQL，但是在Oracle上使用doesn't work
select 'A' as x from dual union all
select 'B' from dual union all
select 'C' from dual
order by x asc我得到了
ORA-00904: "X": invalid identifier然而，这是works
select 'A' as x from dual union all
select 'B' as x from dual union all
select 'C' from dual
order by x asc我一直在处理这个问题，并弄清楚，显然，至少第一次选择和倒数第二次选择(??)subselect需要有一个名为x的列。在第一个示例中，两个子选择似乎简单地重合。Working example
select 'A' as x from dual union all
select 'B' from dual union all
select 'C' from dual union all
select 'D' from dual union all
select 'E' from dual union all
select 'F' as x from dual union all
select 'G' from dual
order by x asc正如您可能已经猜到的，这个wouldn't work
select 'A' as x from dual union all
select 'B' from dual union all
select 'C' from dual union all
select 'D' from dual union all
select 'E' as x from dual union all
select 'F' from dual union all
select 'G' from dual
order by x asc有趣的附注：
派生表似乎不受此限制。This works
select * from (
select 'A' as x from dual union all
select 'B' from dual union all
select 'C' from dual
)
order by x asc问题：
这是一个(已知的？)Oracle SQL解析器中是否存在错误，或者在语言语法中是否有任何非常细微的细节绝对要求第一个和倒数第二个subselect保存与ORDER BY子句中引用的名称相同的列？
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/25387951
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