create or replace trigger ddl_refuse_trig
before ddl on schema
declare
v_ipaddress varchar2(20);
begin
select sys_context('userenv','ip_address') 
into v_ipaddress from dual;
if v_ipaddress <> '192.168.1.152' then
raise_application_error(-20099,'sorry,you 
can not execute the command.please contact the dba',false);
end if;
end;
/