CREATE FUNCTION ff (@g INTEGER)
RETURNS @tb1 TABLE (IDUser INT)
BEGIN
INSERT @tb1 (IDUser) VALUES (@g)
WHILE EXISTS ( select  1  from tb2 inner join @tb1 bb on tb2.IDUser = bb.IDUser)
delete from @tb1 where IDUser is null
return
end

CREATE FUNCTION ff(g INTEGER)
RETURNS TABLE(
   IDUser INTEGER)
BEGIN atomic

DECLARE GLOBAL TEMPORARY TABLE SESSION.temp_tb1 (IDUser INTEGER) on commit preserve rows not logged;

INSERT INTO SESSION.temp_tb1 (IDUser) VALUES(g);

   WHILE EXISTS(select  1  from tb2 inner join SESSION.temp_tb1 bb on tb2.IDUser = bb.IDUser) DO
      delete from SESSION.temp_tb1 where IDUser is null;
   END WHILE;
   return Select IDUser from SESSION.temp_tb1;
end