"su functionality" with sqlplus

Now this sounds a bit unbelievable at first but with 10g R2 "su functionality as we know it from Unixes" can be accomplished.

SQL> create user tester identified by tester;
User created.

SQL> grant connect, resource to tester;
Grant succeeded.

SQL> create user datauser identified by datauser;
User created.

SQL> grant connect, resource to datauser;
Grant succeeded.

SQL> connect datauser/datauser
Connected.

SQL> create table sample(a number);
Table created.

SQL> insert into sample values (99999);
1 row created.

SQL> commit;
Commit complete.

SQL> connect system
Enter password: ******
Connected.

SQL> alter user datauser grant connect through tester;
User altered.

SQL> connect tester[datauser]/tester
Connected.

SQL> show user
USER is "DATAUSER"

SQL> select user from dual;

USER
------------------------------
DATAUSER

SQL> desc sample
Name Null? Type
----------------------------------------- -------- ----------------------------
A NUMBER

SQL> select sys_context('userenv','session_user') "Sess. User",
2 sys_context('userenv','proxy_user') "Prox.User",
3 sys_context('userenv','authentication_type') "Auth.type" from dual;

Sess. User Prox.User Auth.type
-------------------- -------------------- ----------
DATAUSER TESTER PROXY