Update a running total field in table 1 from column in table 2

[tamilselvan]

UPDATE ap_inv a SET tot_1= tot_1 + (select inv_tot_amount from vn_inv v (Select v.inv_num, v.po_num from vn_inv v where a.inv_num=v.inv_num AND a.po_num=v.po_num));

UPDATE ap_inv a 
    SET tot_1= tot_1 + 
                    (select inv_tot_amount 
                       from vn_inv v,
                        (Select v.inv_num, v.po_num
                            from vn_inv v 
                           where a.inv_num=v.inv_num AND 
                            a.po_num=v.po_num
                        )
                     );

Comma missing.

Tamil