WHEN MATCHED THEN
      UPDATE SET
         d.f3= insertlog(s.f3, ....),
         d.f4 = ...
      WHERE d.f5 ...
      

create table TMP_A1(a1 number, a2 varchar2(64))
/
create table TMP_L1(a1 number, a2 varchar2(64))
/
 

create or replace function TestINS(a number, b varchar2) return number
is
begin
   insert into TMP_L1(A1, A2)
   values(a, b);
   return a;
end;
/


delete tmp_a1;
delete tmp_l1;

insert into TMP_A1(a1, a2)
select TestINS(SEQ__A.NEXTVAL, 'xxx'), 'aaa'
  from DUAL
/


select * from TMP_A1
/
select * from TMP_L1  
/  

delete tmp_a1;

1 row deleted

delete tmp_l1;

1 row deleted

insert into TMP_A1(a1, a2)
select TestINS(SEQ__A.NEXTVAL, 'xxx'), 'aaa'
  from DUAL
/

1 row inserted

select * from TMP_A1
/

        A1 A2
---------- ----------------------------------------------------------------
   1795025 aaa
select * from TMP_L1
/

        A1 A2
---------- ----------------------------------------------------------------
   1795025 xxx

create table TMP_A1(a1 number, a2 varchar2(64))
/
create table TMP_L1(d date, a1 number, log1 varchar2(64))
/
 

create or replace function TestINS(a2 varchar2, a1 number, log1 varchar2) return varchar2
is
begin
   insert into TMP_L1(D, a1, log1)
   values(sysdate, a1, log1);
   return a2;
end;
/



merge into tmp_a1 d
using (select 11 a1, 'aaa' a2, 'mylog' log1 from DUAL) s
on (s.a1 = d.a1)
WHEN MATCHED THEN
      UPDATE SET
         d.a2 = TestINS(s.a2, s.a1, s.log1)
    WHEN NOT MATCHED THEN
      INSERT
        (d.a1,d.a2)
      VALUES
        (s.a1, TestINS(s.a2, s.a1, s.log1))