OPS$ORACLE@repo SQL> create table dropme ( x number,y number);

Table created.

OPS$ORACLE@repo SQL> insert into dropme values ( &1, &2 );
Enter value for 1: 22
Enter value for 2: 33
old   1: insert into dropme values ( &1, &2 )
new   1: insert into dropme values ( 22, 33 )

1 row created.

OPS$ORACLE@repo SQL> /
Enter value for 1: 55
Enter value for 2: 66
old   1: insert into dropme values ( &1, &2 )
new   1: insert into dropme values ( 55, 66 )

1 row created.

OPS$ORACLE@repo SQL> commit;

Commit complete.

OPS$ORACLE@repo SQL> select * from dropme;

         X          Y
---------- ----------
        22         33
        55         66

OPS$ORACLE@repo SQL> update (select x,y from dropme) set x=y, y=x;

2 rows updated.

OPS$ORACLE@repo SQL> select * from dropme;

         X          Y
---------- ----------
        33         22
        66         55

OPS$ORACLE@repo SQL>