为了使事情更清楚一点，您可能需要考虑删除审计表中的旧列，并使用一个操作标志（I= UPDATE，U=UPDATE，D= UPDATE）。请参见下文。

ALTER SESSION SET NLS_DATE_FORMAT = 'DD-MON-YYYY HH24:MI:SS';

create table Users ( 
 username varchar2(30) not null constraint users_pk primary key,
 first_name varchar2(30) not null,
 last_name varchar2(30), 
 age number not null
 );

CREATE TABLE  users_audit
(   
    aud_who VARCHAR2 (30),
    aud_when DATE,
    aud_operation VARCHAR2(1),  
    username varchar2(30),
    first_name varchar2(30),
    last_name varchar2(30), 
    age number
    );
/

create or replace
   trigger users_aud_trg
    after insert or update or delete on users 
    for each row
    declare
      l_operation varchar2(1) :=
          case when updating then 'U'
               when deleting then 'D'
               else 'I' end;
   begin
     if updating or inserting then
         insert into users_audit
           (aud_who,
           aud_when,
           aud_operation,
            username,
            first_name,
            last_name,
            age)
         values    (sys_context('USERENV', 'OS_USER'),
           sysdate,
           l_operation,            
         :new.username,                             
         :new.first_name,
         :new.last_name,
         :new.age );
     else
         insert into users_audit
           (aud_who,
           aud_when,
           aud_operation, 
            username,
            first_name,
            last_name,
            age)
         values  (sys_context('USERENV', 'OS_USER'),
           sysdate,
           l_operation,             
          :old.username,
          :old.first_name,
          :old.last_name,
          :old.age);
     end if;
  end
users_aud_trg;
/

INSERT INTO USERS VALUES('ME', 'John', 'Doe', 37);
     
UPDATE USERS SET AGE=40;

DELETE USERS WHERE USERNAME ='ME';

SELECT * FROM users_audit;