oracle服务器没有建立目标数据库的TNS时，在客户端（有权限的情况下）建立dblink语法如下：
create database link dblink_name connect to user_name identified by user_psw using
'(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = xxx.xx.xxx.xx)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = orcl)
)
)'
