To select the Oracle version:

- Connect to the database using SQL*plus

COMMAND:

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle8i Enterprise Edition Release 8.1.7.3.0 - Production
PL/SQL Release 8.1.7.3.0 - Production
CORE 8.1.7.2.1 Production
TNS for 32-bit Windows: Version 8.1.7.3.0 - Production
NLSRTL Version 3.4.1.0.0 - Production

Also the current version is embedded in the Instance name.

How to find the Instance name and Host of an Oracle Database
Definition: The Oracle Instance is the group of processes and memory resources to make the database works.

COMMAND:
SQL> select * from V$instance;

INSTANCE_NUMBER INSTANCE_NAME
---------------                 ----------------
1                                     dje HOST_NAME
----------------------------------------------------------------
MYHOSTNAME

VERSION STARTUP_T STATUS PAR THREAD# ARCHIVE LOG_SWITCH
----------------- --------- ------- --- ---------- ------------------

8.1.7.3.0 08-MAY-06 OPEN NO 1 STARTED

LOGINS SHU DATABASE_STATUS INSTANCE_ROLE

---------- --- ----------------- ------------------

ALLOWED NO ACTIVE PRIMARY_INSTANCE