SQL - Loop block update

block-update.sql

--- template, adjust accordingly
declare
  cnt integer;
begin
	cnt := 0;
	
	for req in (select rowid, x, y, z from tabela where x is null) loop
	
		update tabela set y = x+z where rowid = req.rowid;
		
		cnt := cnt + 1;
		
		if cnt > 5000 then
		  commit;
		  cnt := 0;
		end if;
		
	end loop;
	
	commit;
end;