Update multiple data dengan cursor pada pgsql

tolong bantu saya mau update stock barang dengan menggunakan stored procedure, tapi datanya tidak berubah padahal tidak ada yang error

CREATE or replace FUNCTION SP_PROSES_STOCK(noresep bigint, p_post_cd varchar)
RETURNS void
LANGUAGE plpgsql
as $function$
DECLARE cursorData refcursor;
		v_item_cd varchar;
		v_quantity numeric;

begin
--	v_item_cd :='P005';


	-- hitung data non racik
	open cursorData FOR
 	select A.item_cd, A.quantity from trx_medical_resep B
	inner join trx_resep_data A on A.medical_resep_seqno = B.medical_resep_seqno
	where B.medical_resep_seqno = noresep;
	fetch next from cursorData into v_item_cd,v_quantity;
	while (found)
	loop
		update inv_pos_item set quantity = quantity - v_quantity
		where item_cd = v_item_cd and pos_cd = p_post_cd;
	end loop;
	close cursorData;

END
$function$