Oracle如何实现跨库查询

create public database link dblink
  connect to totalplant identified by totalplant 
  using '(DESCRIPTION =
    (ADDRESS_LIST =
     (ADDRESS = (PROTOCOL = TCP)(HOST = LOCALHOST)(PORT = 1521))
    )
    (CONNECT_DATA =
     (SERVICE_NAME = prd.gdc)
    )
    )';

     using '(DESCRIPTION =
       (ADDRESS_LIST =
        (ADDRESS = (PROTOCOL = TCP)(HOST = 要连接的数据库所在服务器的IP地址)(PORT = 1521))
       )
       (CONNECT_DATA =
        (SERVICE_NAME = 要连接的数据库的在本地的服务名(即要连接的数据库的SID))
       )
       )';

  create database link dblink
  connect to totalplant identified by totalplant 
  using '(DESCRIPTION =
    (ADDRESS_LIST =
     (ADDRESS = (PROTOCOL = TCP)(HOST = LOCALHOST)(PORT = 1521))
    )
    (CONNECT_DATA =
     (SERVICE_NAME = prd.gdc)
    )
    )'; 

select * from tbl_ost_notebook@dblink;

select * from dba_db_links; 

SELECT DISTINCT PRIVILEGE AS "Database Link Privileges"
  FROM ROLE_SYS_PRIVS
  WHERE PRIVILEGE IN ( 'CREATE SESSION','CREATE DATABASE LINK',
        'CREATE PUBLIC DATABASE LINK');