清除db_link笔记

1. 查询使用使用perfstat和system账号的dblink:
   select * from dba_db_links where username in ('PERFSTAT','SYSTEM');
2. 删除使用perfstat和system账号的dblink：
   drop database link db_link_name;
3. 确认已删除使用perfstat和system账号的dblink:
   select * from dba_db_links where username in ('PERFSTAT','SYSTEM');
4. 清除不在自己名下的db_link

alter user scott grant connect through test;
CONN test[scott]/test_pw
select 1 from dual@dblink_name;  #测试连通性，不连通则删
alter user scott revoke connect through test