Triggers, are PL/SQL code that runs:
        
        Before/After 
        an Insert/Update/Delete
        
        :NEW <- the data being inserted or updated
        :OLD <- the exist data for an update or delete
        
                create table Sample(
                  id integer primary key,
                  data varchar(25),
                  created_by varchar(12),
                  created_date date)
        
        commit;
        
        CREATE OR REPLACE TRIGGER sample_bi
        BEFORE INSERT ON Sample
        FOR EACH ROW
        
        BEGIN
          :NEW.created_by := USER;
          :NEW.created_date := SYSDATE;
        END;