ORA-38104:无法更新ON子句中引用的列

Question

我有一个带删除标志的简单表(记录应该在此列中更新而不是删除):

create table PSEUDODELETETABLE
(
  ID        NUMBER(8) not null, -- PKEY
  NAME      VARCHAR2(50) not null,
  ISDELETED NUMBER(1) default 0 not null
)

插入新记录时,我必须检查是否已存在与主键匹配但是ISDELETED = 1的记录.在这种情况下,我必须将ISDELETED更改为0并更新其他列.因此我使用以下Merge-Statement:

merge into ET.PSEUDODELETETABLE TARGET
using (select 1 as ID, 'Horst' as NAME from sys.dual) SOURCE
on (TARGET.ISDELETED = 1 and SOURCE.ID = TARGET.ID)
when matched then
  update set ISDELETED = 0, NAME = SOURCE.NAME
when not matched then
  insert values (SOURCE.ID, SOURCE.NAME, 0);

在Sql-Server上它运行良好,但Oracle说:

ORA-38104: Columns referenced in the ON Clause cannot be updated: TARGET.ISDELETED

如果存在IDELETED = 0的匹配记录,我希望将主键冲突作为例外,这就是为什么我不能将"TARGET.ISDELETED = 1"从on-clause移动到update-statement.

Answer 1

与接受的响应相反,实际上有一种方法可以解决这个问题:将违规位移出ON子句并进入update语句的WHERE子句:

merge into ET.PSEUDODELETETABLE TARGET
using (select 1 as ID, 'Horst' as NAME from sys.dual) SOURCE
on (SOURCE.ID = TARGET.ID)
when matched then
  update 
      set ISDELETED = 0, 
      NAME = SOURCE.NAME
  where TARGET.ISDELETED = 1 -- Magic!
when not matched then
  insert 
      values (SOURCE.ID, SOURCE.NAME, 0);

Answer 2

将列放入某种表达式中并重命名似乎可行。在下面的示例中，ISDELETED_和ISDELETED实际上是同一件事：

merge into (
  select nvl(ISDELETED, ISDELETED) as ISDELETED_, ISDELETED, ID, 
  from ET.PSEUDODELETETABLE
) TARGET
using (select 1 as ID, 'Horst' as NAME from sys.dual) SOURCE
on (TARGET.ISDELETED_ = 1 and SOURCE.ID = TARGET.ID) -- Use the renamed version here
when matched then
  update set ISDELETED = 0, NAME = SOURCE.NAME       -- Use the original version here
when not matched then
  insert values (SOURCE.ID, SOURCE.NAME, 0);

注意：

• 仅仅重命名是不行的。解析器似乎足够“聪明”，可以检测到它仍然是同一列。但是重命名并将其放入“愚蠢”的表达式中会比解析器更聪明。
• 这显然是有代价的。索引可能无法在重命名的列上轻松使用，请检查执行计划。在这个特定的例子中，它可能会起作用
• Oracle 将来可能会“修复”此问题（并使 ORA-38104 检测更加一致），因此此解决方法可能会失效。

这似乎也有效，但绝对似乎不允许任何合理的索引使用（请再次检查您的 Oracle 版本）：

merge into ET.PSEUDODELETETABLE TARGET
using (select 1 as ID, 'Horst' as NAME from sys.dual) SOURCE
on ((select TARGET.ISDELETED from dual) = 1 and SOURCE.ID = TARGET.ID)
when matched then
  update set ISDELETED = 0, NAME = SOURCE.NAME
when not matched then
  insert values (SOURCE.ID, SOURCE.NAME, 0);

即使这样也有效（这引发了对整个 ORA-38104 检查的严重怀疑）！

merge into ET.PSEUDODELETETABLE TARGET
using (select 1 as ID, 'Horst' as NAME from sys.dual) SOURCE
on ((TARGET.ISDELETED, 'dummy') = ((1, 'dummy')) and SOURCE.ID = TARGET.ID)
when matched then
  update set ISDELETED = 0, NAME = SOURCE.NAME
when not matched then
  insert values (SOURCE.ID, SOURCE.NAME, 0);

我已经在博客中介绍了这些解决方法（和执行计划）。

Answer 3

我怀疑在这种情况下，使用先拍后看的算法会更好。

根据您预计更常见的情况，可以选择：

• 更新，如果没有更新行，则插入；或者
• 插入，如果有关键违规，则更新。