SQL & PL/SQL

UPDATE (SELECT t1.ax_index a1, t2.ax_index b1 
                                          FROM aa t1, bb t2 
                                                WHERE 
                                                    t1.trade_no_tri = t2.trade_jul||t2.trade_no 
                                                    and t1.sec_no=t2.sec_no 
                                                    and t_account=f_acct
                                                    and t1.cust_acct=t2.cust_acct 
                                                    and t1.quantity=t2.quantity
                                                    and rept_amt=principal            
                                                    and t2.source='aaa'
                                                   and  rownum=1) SET a1 = b1;