接下来的Oracle数据库学习教程要告诉大家的是关于Oracle同时访问多个SQL Server的方法。大家可以认真地学习一下：
ORACLE 是以高级结构化查询语言(SQL)为基础的大型关系数据库，通俗地讲它是用方便逻辑管理的语言操纵大量有规律数据的集合。是目前最流行的客户/服务器(CLIENT/SERVER)体系结构的数据库之一。那么如何使Oracle能同时访问多个SQL Server呢？下面便为它解答：
1、在安装了Oracle9i Standard Edition或者Oracle9i EntERPrise Edition的Windows机器上(IP:192.168.0.2), 产品要选了透明网关(Oracle Transparent Gateway)里访问Microsoft SQL Server数据库。
ORACLE9I_HOME\\tg4msql\\admin下新写initpubs.ora和initnorthwind.ora配置文件。
initpubs.ora内容如下：
HS_FDS_CONNECT_INFO="SERVER=SQLSERVER_HOSTNMAE;DATABASE=pubs"
HS_DB_NAME=pubsHS_FDS_TRACE_LEVEL=OFF
HS_FDS_RECOVERY_ACCOUNT=RECOVER
HS_FDS_RECOVERY_PWD=RECOVER
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initnorthwind.ora内容如下：
HS_FDS_CONNECT_INFO="SERVER=sqlserver_hostname;DATABASE=Northwind"
HS_DB_NAME=Northwind
HS_FDS_TRACE_LEVEL=OFF
HS_FDS_RECOVERY_ACCOUNT=RECOVER
HS_FDS_RECOVERY_PWD=RECOVER
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$ORACLE9I_HOME\\network\\admin 下listener.ora内容如下：
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST =
192.168.0.2)(PORT = 1521))
)
)
)
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = test9)
(ORACLE_HOME = d:\\oracle\\ora92)
(SID_NAME = test9)
)
(SID_DESC=
(SID_NAME=pubs)
(ORACLE_HOME=d:\\Oracle\\Ora92)
(PROGRAM=tg4msql)
)
(SID_DESC=
(SID_NAME=northwind)
(ORACLE_HOME=d:\\Oracle\\Ora92)
(PROGRAM=tg4msql)
)
)
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重启动这台做gateway的Windows机器上(IP:192.168.0.2)TNSListener服务(凡是按此步骤新增可访问的SQL Server数据库系统时，TNSListener服务都要重启动)。
2、Oracle8i，Oracle9i的服务器端配置tnsnames.ora, 添加下面的内容：
pubs =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.2)(PORT = 1521))
)
(CONNECT_DATA =
(SID = pubs)
)
(HS = pubs)
)
northwind =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.2)(PORT = 1521))
)
(CONNECT_DATA =
(SID = northwind)
)
(HS = northwind) )
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保存tnsnames.ora后，在命令行下：
tnsping pubs
tnsping northwind
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出现类似提示，即为成功：
Attempting to contact (DESCRIPTION = (ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.2)
(PORT = 1521))) (CONNECT_DATA = (SID = pubs)) (HS = pubs))
OK（20毫秒）
Attempting to contact (DESCRIPTION = (ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.2)
(PORT = 1521)))
(CONNECT_DATA = (SID = northwind)) (HS = northwind))OK（20毫秒）
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设置数据库参数global_names=false。
设置global_names=false不要求建立的数据库链接和目的数据库的全局名称一致。global_names=true则要求, 多少有些不方便。
oracle9i和oracle8i都可以在DBA用户下用SQL命令改变global_names参数：
alter system set global_names=false;
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建立公有的数据库链接：
create public database link pubs
connect to testuser identified by testuser_pwd using 'pubs';
create public database link northwind
connect to testuser identified by testuser_pwd using 'northwind';
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#p#分页标题#e#
(假设SQL Server下pubs和northwind已有足够权限的用户登陆testuser,密码为testuser_pwd)
访问SQL Server下数据库里的数据：
select * from stores@pubs;
...... ......select *
from region@northwind;
...... ......
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3、使用时的注意事项
ORACLE通过访问SQL Server的数据库链接时，用select * 的时候字段名是用双引号引起来的。例如：
create table stores as select * from stores@pubs;
select zip from stores；
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ERROR 位于第 1 行：
ORA-00904: 无效列名
select "zip" from stores;
zip
-----
98056
92789
96745
98014
90019
89076
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已选择6行，用SQL Navigator或Toad看从SQL Server转移到ORACLE里的表的建表。语句为：
CREATE TABLE stores
("stor_id" CHAR(4) NOT NULL,
"stor_name" VARCHAR2(40),
"stor_address" VARCHAR2(40),
"city" VARCHAR2(20),
"state" CHAR(2),
"zip" CHAR(5))
PCTFREE 10
PCTUSED 40
INITRANS 1
MAXTRANS 255
TABLESPACE users
STORAGE (
INITIAL 131072
NEXT 131072
PCTINCREASE 0
MINEXTENTS 1
MAXEXTENTS 2147483645
)
/
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总结：
Windows下Oracle9i网关服务器在$Oracle9i_HOME\\tg4msql\\admin目录下的initsqlserver_databaseid.ora。Windows下Oracle9i网关服务器listener.ora里面：
(SID_DESC=
(SID_NAME=sqlserver_databaseid)
(ORACLE_HOME=d:\\Oracle\\Ora92)
(PROGRAM=tg4msql)
)
Unix或WINDOWS下ORACLE8I,ORACLE9I服务器tnsnames.ora里面
northwind =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.2)(PORT = 1521))
)
(CONNECT_DATA =
(SID = sqlserver_databaseid)
)
(HS = sqlserver_databaseid)
)
|
需要sqlserver_databaseid一致才行。
好了，具体内容就讲到这里。更多相关的Oracle教学视频尽在课课家官方网。
