Oracle CASE语句报ORA-00923错误，SQL Dev正常但代码调用失败

我编写了如下Oracle查询语句：

SELECT
  CASE WHEN P.ORGINAL_PROSJEKT_K IS NULL
  THEN RAD_LAGER
  ELSE (
    SELECT PO.RAD_LAGER
    FROM PROSJEKT PO
    WHERE PO.PROSJEKT_K = P.ORGINAL_PROSJEKT_K
  ) END AS RAD_LAGER_ORIGINAL
  FROM PROSJEKT P
  WHERE P.PROSJEKT_K = PROSJEKT_K;

这条语句在SQL Developer中可正常执行，但通过C#代码调用时触发InnerException: ORA-00923 FROM keyword not found where expected错误。我尝试过给别名RAD_LAGER_ORIGINAL加引号、修改别名不含下划线，但均无效。

我使用NHibernate进行映射，相关代码如下：

Map(x => x.ProsjektLagetAv).Formula(@"(SELECT CASE WHEN P.ORGINAL_PROSJEKT_K IS NULL THEN RAD_LAGER ELSE (SELECT PO.RAD_LAGER FROM PROSJEKT PO WHERE PO.PROSJEKT_K = P.ORGINAL_PROSJEKT_K) END AS RAD_LAGER_ORIGINAL FROM PROSJEKT P WHERE P.PROSJEKT_K = PROSJEKT_K)");

实体构造代码：

[DataMember]
public virtual string ProsjektLagetAv { get; set; }
// PROSJEKT_K参数始终已提供且不为空。

Map(x => x.ProsjektK, "PROSJEKT_K");
[DataMember]
public virtual string ProsjektK { get; set; }

解决方法 #

NHibernate在映射时存在特殊处理，无法识别带别名的子查询结构，移除别名AS RAD_LAGER_ORIGINAL后问题解决，修改后的查询语句如下：

SELECT
  CASE WHEN P.ORGINAL_PROSJEKT_K IS NULL
  THEN RAD_LAGER
  ELSE (
    SELECT PO.RAD_LAGER
    FROM PROSJEKT PO
    WHERE PO.PROSJEKT_K = P.ORGINAL_PROSJEKT_K
  ) END
  FROM PROSJEKT P
  WHERE P.PROSJEKT_K = PROSJEKT_K;

内容的提问来源于stack exchange，提问作者s1dda