create table time_test(
       val varchar2(200),
       ctime varchar2(14)
);
DROP TRIGGER "time_test_TR";

CREATE OR REPLACE TRIGGER "time_test_TR" 
BEFORE INSERT ON time_test
REFERENCING OLD AS "OLD" NEW AS "NEW" FOR EACH ROW 
when (new.ctime IS NULL)
BEGIN
       select to_char(systimestamp,'yyyymmddhh24miss') into :new.ctime from dual;
END;
/

ALTER TRIGGER "time_test_TR" ENABLE;

 insert into time_test(val)values('val1');
insert into time_test(val)values('val2');