Специально для Вас привожу функцию выбирающую дерево:
CREATE FUNCTION F_SELECT_ALL_CONST_NODES(@startid int)
RETURNS @tmp table (id int, parent int, code varchar(20), lev int) AS
BEGIN
declare @i int set @i = 0
insert into @tmp select id, parentid, code, 0 from const where id = @startid
while @@rowcount > 0 begin
set @i = @i + 1
insert into @tmp select o.id, o.parentid, o.code, @i from const o inner join @tmp t on t.lev = @i - 1 and o.parentid = t.id
order by lev, o.id
end
return
END
далее
update Table set field = value

where id in (select id from моя_функция)