CREATE TABLE TEST_TABLE
    (id                             NUMBER( 38 , 0 ) NOT NULL,
     code                       VARCHAR2( 32 ) NOT NULL
     )
/
CREATE SEQUENCE test_seq
  INCREMENT BY  1 
  START WITH  1 
  MINVALUE  1 
  MAXVALUE  999999999999999999999999999 
  NOCYCLE
  NOORDER
  NOCACHE
/
CREATE OR REPLACE TRIGGER test_trig_BIR
 BEFORE
  INSERT
 ON Test_TABLE
REFERENCING NEW AS NEW OLD AS OLD
 FOR EACH ROW
begin 
if :new.id is null then
select test_seq.nextval 
into :new.id
from sys.dual;
end if;
end;
/