create table src(seq number ,len number);
 
create table dest(mod varchar2(1),out varchar2(1),
sequence number , length number);
 
create or replace trigger trig1
after insert or update or delete
of seq,len
on src
referencing new as new old as old
for each row
declare
vseq src.seq%type;
vlen src.len%type;
vmod varchar2(1);
vout varchar2(1);
begin
 
if updating ('seq') or inserting then
vseq:=:new.seq;
vlen:=:new.len;
vmod:='i';
vout:='n';
insert into dest(mod,out,sequence,length) values(vmod,vout,vseq,vlen);
end if;
 
if updating('seq') or deleting then
vseq:=:old.seq;
vlen:=:old.len;
vmod:='d';
vout:='y';
insert into dest(mod,out,sequence,length) values(vmod,vout,vseq,vlen);
end if;
 
if updating('len') then
vseq:=:new.seq;
vlen:=:new.len;
vmod:='u';
vout:='n';
insert into dest(mod,out,sequence,length) values(vmod,vout,vseq,vlen);
end if;
end;

SQL> insert into src values(1,2);
 
1 row created.
 
SQL> select * from src;
 
       SEQ        LEN
---------- ----------
         1          2
 
SQL> select * from dest;
 
M O   SEQUENCE     LENGTH
- - ---------- ----------
i n          1          2
 
SQL> update src set seq=2;
 
1 row updated.
 
SQL> select * from dest;
 
M O   SEQUENCE     LENGTH
- - ---------- ----------
i n          1          2
i n          2          2
d y          1          2
 
SQL> update src set len=3;
 
1 row updated.
 
SQL> select * from dest;
 
M O   SEQUENCE     LENGTH
- - ---------- ----------
i n          1          2
i n          2          2
d y          1          2
u n          2          3
 
SQL> delete from src;
 
1 row deleted.
 
SQL> select * from dest;
 
M O   SEQUENCE     LENGTH
- - ---------- ----------
i n          1          2
i n          2          2
d y          1          2
u n          2          3
d y          2          3
 
SQL> 

begin
  if updating('seq') then
     if inserting then
        vseq:=:new.seq;
        vlen:=:new.len;
        vmod:='i';
        vout:='n';
     elsif deleting then
        vseq:=:old.seq;
        vlen:=:old.len;
        vmod:='d';
        vout:='y';
     end if;
  elsif updating('len') then
     vseq:=:new.seq;
     vlen:=:new.len;
     vmod:='u';
     vout:='n';
  end if;

  insert into dest(mod,out,sequence,length) values(vmod,vout,vseq,vlen);
end;

begin
   if updating ('seq') or inserting then
      insert into dest(mod,out,sequence,length)
         values('i','n',:new.seq,:new.len);
   end if;
 
   if updating('seq') or deleting then
      insert into dest(mod,out,sequence,length)
        values('d','y',:old.seq,:old.len);
   end if;
 
  if updating('len') then
      insert into dest(mod,out,sequence,length)
         values('u','n',:new.seq,:new.len);
   end if;
end;