使用触发器实现数据库级守护,防止DDL操作
http://www.eygle.com/archives/2004/12/use_trigger_to_implement_ddl_deny.html

不管是有意还是无意的,你可能会遇到数据库中重要的数据表等对象被drop掉的情况,这可能会给我们带来巨大的损失.

通过触发器，我们可以实现对于表等对象的数据库级守护，禁止用户drop操作.

以下是一个简单的范例，供参考:

REM this script can be used to monitor a object
REM deny any drop operation on it.
CREATE OR REPLACE TRIGGER trg_dropdeny
   BEFORE DROP ON DATABASE
BEGIN
   IF LOWER (ora_dict_obj_name ()) = 'test'
   THEN
      raise_application_error (num      => -20000,
                               msg      =>    '你疯了,想删除表 '
                                           || ora_dict_obj_name ()
                                           || ' ?!!!!!'
                                           || '你完了，警察已在途中.....'
                              );
   END IF;
END;
/      
                     
测试效果:

SQL> connect scott/tiger
Connected.
SQL> create table test as select * from dba_users;

Table created.

SQL> connect / as sysdba
Connected.
SQL> create or replace trigger trg_dropdeny
  2     before drop on database  
  3  begin
  4        if lower(ora_dict_obj_name()) = 'test'       
  5        then
  6        raise_application_error(
  7           num => -20000,
  8           msg => '你疯了,想删除表 ' || ora_dict_obj_name() || ' ?!!!!!' ||'你完了，警察已在途中.....');
  9        end if;
10     end;
11  /

Trigger created.

SQL> connect scott/tiger
Connected.
SQL> drop table test;
drop table test
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-20000: 你疯了,想删除表 TEST ?!!!!!你完了，警察已在途中.....
ORA-06512: at line 4
      
Oracle从Oracle8i开始,允许实施DDL事件trigger，可是实现对于DDL的监视及控制,以下是一个进一步的例子:

create or replace trigger ddl_deny
before create or alter or drop or truncate on database
declare
  l_errmsg varchar2(100):= 'You have no permission to this operation';
begin
  if ora_sysevent = 'CREATE' then
     raise_application_error(-20001, ora_dict_obj_owner || '.' || ora_dict_obj_name || ' ' || l_errmsg);
  elsif ora_sysevent = 'ALTER' then
    raise_appl