在实际的操作中你对Oracle中设置访问N个SQL Server数据库的实际操作是否满头雾水？如果我们要在Oracle同时访问N个SQL Server中默认的pubs与Northwind两个数据库。那么我们应该如何操作呢？

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据库

ORACLE9I_HOMEtg4msqladmin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

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 
$ORACLE9I_HOMEnetworkadmin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:oracleora92) 
(SID_NAME=test9) 
) 
(SID_DESC= 
(SID_NAME=pubs) 
(ORACLE_HOME=d:OracleOra92) 
(PROGRAM=tg4msql) 
) 
(SID_DESC= 
(SID_NAME=northwind) 
(ORACLE_HOME=d:OracleOra92) 
(PROGRAM=tg4msql) 
) 
)

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))

保存tnsnames.ora后,在命令行下

tnspingpubs 
tnspingnorthwind 

出现类似提示，即为成功:

Attemptingtocontact(DESCRIPTION=(ADDRESS_LIST= 
(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.0.2) 
(PORT=1521)))(CONNECT_DATA=(SID=pubs))(HS=pubs)) 
OK（20毫秒） 
Attemptingtocontact(DESCRIPTION=(ADDRESS_LIST= 
(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.0.2) 
(PORT=1521))) 
(CONNECT_DATA=(SID=northwind))(HS=northwind))OK（20毫秒）

Oracle同时访问中设置数据库参数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

altersystemsetglobal_names=false;

建立公有的数据库链接:

createpublicdatabaselinkpubs 
connecttotestuseridentifiedbytestuser_pwdusing'pubs'; 
createpublicdatabaselinknorthwind 
connecttotestuseridentifiedbytestuser_pwdusing'northwind';

(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*fromstores@pubs; 
............select* 
fromregion@northwind;

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：

createtablestoresasselect*fromstores@pubs; 
selectzipfromstores；

ERROR 位于第 1 行:ORA-00904: 无效列名

select"zip"fromstores; 
zip 
----- 
98056 
92789 
96745 
98014 
90019 
89076

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:

CREATETABLEstores 
("stor_id"　CHAR(4)NOTNULL, 
"stor_name"VARCHAR2(40), 
"stor_address"VARCHAR2(40), 
"city"VARCHAR2(20), 
"state"CHAR(2), 
"zip"　CHAR(5)) 
PCTFREE10 
PCTUSED40 
INITRANS1 
MAXTRANS255 
TABLESPACEusers 
STORAGE( 
INITIAL131072 
NEXT131072 
PCTINCREASE0 
MINEXTENTS1 
MAXEXTENTS2147483645 
)

总结: Windows下Oracle9i网关服务器在$Oracle9i_HOMEtg4msqladmin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:OracleOra92) 
(PROGRAM=tg4msql) 
)