Users normally use the "connect" statement to connect from one
database user to another. However, DBAs can switch from one user to
another without a password. Of course it is not advisable to bridge
Oracle's security, but look at this example: SQL> select password from
dba_users where username='SCOTT';
PASSWORD
F894844C34402B67
SQL> alter user scott identified by lion;
User altered.
SQL> connect scott/lion
Connected.
REM Do whatever you like...
SQL> connect system/manager
Connected.
SQL> alter user scott identified by values 'F894844C34402B67';
User altered.
SQL> connect scott/tiger
Connected.
Note: Also see the su.sql script in the Useful Scripts and Sample
Programs Page.