建立数据库链接 create database link

删除数据库链接：drop database link linkname;

创建数据库链接：
create database link linkname
connect to username
identified by password
using 'connection string';


如果想建立全局链接，则需要使用关键字：public

create public database link linkname
connect to username
identified by password
using 'connection string';


connection string可以有两种形式：
1，在文件tnsnames.ora配置的名称：
如：
CDRDL =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.147.129.29)(PORT = 2521))
)
(CONNECT_DATA =
(SERVICE_NAME = cdrdb)
)
)
此时可以写成：
create database link linkname
connect to username
identified by password
using 'CDRDL ';

2，也可以直接使用‘=’号后面的字符串，
如：
create database link linkname
connect to username
identified by password
using '(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=10.147.129.29)(PORT=2521)))(CONNECT_DATA=(SERVICE_NAME=cdrdb))) ';