10g 和 11g 之间的 Oracle 数据库链接
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Oracle database links between 10g and 11g
提问by JavaRocky
Does anyone have experience with database links between 10g and 11g?
有没有人对 10g 和 11g 之间的数据库链接有经验？
Is this a supported setup/operation? Is it possible? Are there any problems? Caveats?
这是受支持的设置/操作吗？是否可以？有什么问题吗？注意事项？
回答by Gary Myers
I've been using DB Links from 11g to 10g. No big issues.
我一直在使用从 11g 到 10g 的数据库链接。没什么大问题。
Only caveat is that 11g can use mixed-case passwords and you might want to switch that off if you are trying to connect from a 10g database to an 11g one.
唯一需要注意的是 11g 可以使用大小写混合的密码，如果您尝试从 10g 数据库连接到 11g 数据库，您可能需要关闭它。
回答by Deon Steyn
A view with dblink in the select list can no longer be accessed from another schema via a synonym (used to work in Oracle 10)
选择列表中带有 dblink 的视图不能再通过同义词从另一个模式访问（用于在 Oracle 10 中工作）
The view
风景
create or replace foo_view as
select foo.id@link id --yes, I know this is stupid... legacy code
from foo@link
On other DB user
在其他数据库用户上
create synonym foo_synonym for otherdb.foo_view
select foo_synonym: "ORA-02019 connection description for remote database not found"
select foo_synonym: "ORA-02019 找不到远程数据库的连接描述"
The solution is to remove dblinks from the underlying view's select clause (which shouldn't really be there in the first place):
解决方案是从底层视图的 select 子句中删除 dblinks（首先它不应该真正存在）：
create or replace foo_view as
select foo.id id
from foo@lin foo
回答by dba.in.ua
Sometimes there are problems, when a link from 11G to 10.2.0.4.
有时候会出现问题，从11G连接到10.2.0.4的时候。
Oracle Support Doc ID 730423.1: Select With Local Function and Remote Tables Using a Dblink Hangs Due To Enq DX.
Oracle 支持文档 ID 730423.1：由于 Enq DX，使用 Dblink 使用本地函数和远程表进行选择挂起。
回答by Graydon Mah
ORA-01719 can also be thrown if you have an outer join query in 11g that also uses IN or OR and the tables are being referenced through a db_link to 10g.
如果您在 11g 中有一个也使用 IN 或 OR 的外连接查询，并且表正通过 db_link 引用到 10g，则也可能抛出 ORA-01719。
11g to 11g works as does 10g to 10g - just comes up if you db_link from 11g to 10g.
11g 到 11g 和 10g 到 10g 一样工作 - 如果你 db_link 从 11g 到 10g 就会出现。
Specifically, I'm currently seeing this issue using 11.2.0.1 to 10.2.0.3; and 11.2.0.2 to 10.2.0.4. As well as varying O/S releases: Windows and Solaris.
具体来说，我目前正在使用 11.2.0.1 到 10.2.0.3 看到这个问题；和 11.2.0.2 到 10.2.0.4。以及不同的操作系统版本：Windows 和 Solaris。
Run this in the target 10g and 11g databases:
在目标 10g 和 11g 数据库中运行：
create table u1 (c1 number);
create table u2 (c1 number, c2 number);
insert into u1 values (1);
insert into u1 values (2);
insert into u2 values (1,1);
insert into u2 values (1,2);
commit;
Create db_links (DB10, DB11) in your 11g linking database to both the 10g and 11g linked databases.
在 11g 链接数据库中创建 db_links（DB10、DB11）到 10g 和 11g 链接数据库。
Run these queries in your 11g linking database:
在 11g 链接数据库中运行这些查询：
/* this will fail 11g to 10g*/
SELECT *
FROM u1@DB10 a,
(SELECT *
FROM u2@DB10
WHERE c1 IN (1, 2, 3)) b
WHERE a.c1 = b.c1(+);
/* this will work 11g to 11g*/
SELECT *
FROM u1@DB11 a,
(SELECT *
FROM u2@DB11
WHERE c1 IN (1, 2, 3)) b
WHERE a.c1 = b.c1(+);
