oracle数据库在拥有create session权限下默认对所创建的对象有drop and alter权限，这些权限我们不能revoke，我们可以通过以下触发器来控制普通用户这些权限，来满足部分安全上的需要

CREATE OR REPLACE TRIGGER trg_dropdeny
before drop on database
begin
if (ora_login_user!='SYS' and ora_login_user!='SYSTEM')
then
raise_application_error(
num=>-20000,
msg=>'You can not drop ' || ora_dict_obj_name() || ' ! please ask dba to finish version control.thank you1');
end if;
end;

CREATE OR REPLACE TRIGGER trg_alterdeny
before alter on database
begin
if (ora_login_user!='SYS' and ora_login_user!='SYSTEM')
then
raise_application_error(
num=>-20000,
msg=>'You can not drop ' || ora_dict_obj_name() || ' ! please ask dba to finish version control.thank you1');
end if;
end;