ENTITY = '001' AND DEAL_NO = '12345'

STEP_ID = 'la-la'

update 
(
select STEP_ID, rownumber() over (order by timestamp desc) rn
from a
WHERE ENTITY = '001' AND DEAL_NO = '12345'
) t
set STEP_ID = 'la-la'
where rn= 1 ;

begin atomic

declare sqlcode int default  0 ;
declare lSTEP_ID VARCHAR( 10 );
declare lrn int;

declare c1 cursor for
select STEP_ID, rownumber() over (order by timestamp desc) rn
from A
WHERE ENTITY = '001' AND DEAL_NO = '12345';

open c1;
fetch c1 into lSTEP_ID, lrn;
while (sqlcode!= 100 ) do
 if (lrn= 1 ) then
   update a
   set STEP_ID = 'la-la'
   where current of c1;
 end if;
 fetch c1 into lv, lrn;
end while;
close c1;

end@