ORA-01779:无法修改映射到非密钥保留表的列

Question

我有这个程序:

create or replace procedure changePermissionsToRead(
datasource  in varchar2
) 
IS

begin

update 
(
select * from 
WEB_USERROLE ur ,
WEB_USERDATASOURCE ds 
where 
    ur.username = ds.username 
    and 
    ds.datasource = datasource
    and 
    ur.READ_ONLY <> 'Y'  
)
r set r.role = replace(r.role, 'FULL', 'READ');
end;

我收到以下错误:

 ORA-01779

但如果我拿出更新,我写道:

  update 
(
select * from 
WEB_USERROLE ur ,
WEB_USERDATASOURCE ds 
where 
    ur.username = ds.username 
    and 
    ds.datasource = 'PIPPO'
    and 
    ur.READ_ONLY <> 'Y'  
)
r set r.role = replace(r.role, 'FULL', 'READ');

然后这很好用.你能告诉我发生了什么吗？

Answer 1

只有在需要来自多个表的列时,DML表表达式子句才有用.在您的情况下,您可以使用常规更新EXISTS:

update web_userrole
set role = replace(role, 'FULL', 'READ')
where read_only <> 'Y'
    and exists
    (
        select 1/0
        from web_userdatasource
        where datasource = p_datasource
            and username = web_userrole.username
    );

如果您确实需要使用两个表中的列,则有三个选项:

1. 重复SET和和WHERE子句中的连接.这很容易构建,但不是最佳的.
2. DML表表达式.如果你有正确的索引,这应该工作.

3. MERGE,下面是一个例子.

   merge into web_userrole
   using
   (
       select distinct username
       from web_userdatasource
       where datasource = p_datasource
   ) web_userdatasource on
   (
       web_userrole.username = web_userdatasource.username
       and web_userrole.read_only <> 'Y'
   )
   when matched then update
   set role = replace(role, 'FULL', 'READ');
   

这不能直接回答您的问题,而是提供一些解决方法.我无法重现你得到的错误.我需要一个完整的测试用例来进一步研究它.

可更新视图的通用建议

可更新视图的主要问题之一是对它们可以包含的查询的大量限制.查询或视图不得包含许多功能,例如DISTINCT,GROUP BY,某些表达式等.具有这些功能的查询可能会引发异常"ORA-01732:数据操作操作在此视图中不合法".

可更新视图查询必须只明确地返回修改后的表的每一行.查询必须是"密钥保留",这意味着Oracle必须能够使用主键或唯一约束来确保每行只修改一次.

为了说明为什么密钥保留很重要,下面的代码会创建一个不明确的更新语句.它创建了两个表,第一个表有一行,第二个表有两行.表按列连接A,并尝试更新B第一个表中的列.在这种情况下,Oracle阻止更新是好的,否则该值将是非确定性的.有时将值设置为"1",有时将其设置为"2".

--Create table to update, with one row.
create table test1 as
select 1 a, 1 b from dual;

--Create table to join two, with two rows that match the other table's one row.
create table test2 as
select 1 a, 1 b from dual union all
select 1 a, 2 b from dual;

--Simple view that joins the two tables.
create or replace view test_view as
select test1.a, test1.b b_1, test2.b b_2
from test1
join test2 on test1.a = test2.a;

--Note how there's one value of B_1, but two values for B_2.
select *
from test_view;

A  B_1  B_2
-  ---  ---
1    1    1
1    1    2

--If we try to update the view it fails with this error:
--ORA-01779: cannot modify a column which maps to a non key-preserved table
update test_view
set b_1 = b_2;

--Using a subquery also fails with the same error.
update
(
    select test1.a, test1.b b_1, test2.b b_2
    from test1
    join test2 on test1.a = test2.a
)
set b_1 = b_2;

该MERGE声明没有相同的限制.该MERGE语句似乎试图在运行时检测歧义,而不是编译时间.

不幸的是MERGE,并不总能很好地检测出歧义.在Oracle 12.2上,以下语句有时会起作用,然后失败.对查询进行小的更改可能会使其工作或失败,但我找不到特定的模式.

--The equivalent MERGE may work and changes "2" rows, even though there's only one.
--But if you re-run, or uncomment out the "order by 2 desc" it might raise:
--  ORA-30926: unable to get a stable set of rows in the source tables
merge into test1
using
(
    select test1.a, test1.b b_1, test2.b b_2
    from test1
    join test2 on test1.a = test2.a
    --order by 2 desc
) new_rows
    on (test1.a = new_rows.a)
when matched then update set test1.b = new_rows.b_2;

UPDATE如果在理论上可能有重复,则在编译时失败.一些应该运行的语句将无法运行.

MERGE如果数据库在运行时检测到不稳定的行,则会失败 一些不应该工作的陈述仍然会运行.