Originally posted by akhadar
But will give error when u are trying to set one instance and connecting with OS authentication.Try it--
Not True.

PS

Code:
C:\>set oracle_sid=test

C:\>echo %oracle_sid%
test

C:\>sqlplus

SQL*Plus: Release 9.0.1.0.1 - Production on Tue Apr 15 17:10:41 2003

(c) Copyright 2001 Oracle Corporation.  All rights reserved.

Enter user-name: / as sysdba

Connected to:
Oracle9i Enterprise Edition Release 9.0.1.1.1 - Production
With the Partitioning option
JServer Release 9.0.1.1.1 - Production

SQL> select * from global_name;

GLOBAL_NAME
-----------------------------------------------------------------------------------------------
TEST.DOMAIN.NET

SQL> exit
Disconnected from Oracle9i Enterprise Edition Release 9.0.1.1.1 - Production
With the Partitioning option
JServer Release 9.0.1.1.1 - Production

C:\>sqlplus

SQL*Plus: Release 9.0.1.0.1 - Production on Tue Apr 15 17:11:12 2003

(c) Copyright 2001 Oracle Corporation.  All rights reserved.

Enter user-name: sys as sysdba
Enter password:

Connected to:
Oracle9i Enterprise Edition Release 9.0.1.1.1 - Production
With the Partitioning option
JServer Release 9.0.1.1.1 - Production

SQL> select * from global_name;

GLOBAL_NAME
-----------------------------------------------------------------------------------------------
TEST.DOMAIN.NET

SQL> exit
Disconnected from Oracle9i Enterprise Edition Release 9.0.1.1.1 - Production
With the Partitioning option
JServer Release 9.0.1.1.1 - Production

C:\>set oracle_sid=oemrep

C:\>echo %oracle_sid%
oemrep

C:\>sqlplus

SQL*Plus: Release 9.0.1.0.1 - Production on Tue Apr 15 17:12:53 2003

(c) Copyright 2001 Oracle Corporation.  All rights reserved.

Enter user-name: / as sysdba
Connected to an idle instance.

SQL> select * from global_name;
select * from global_name
*
ERROR at line 1:
ORA-01034: ORACLE not available -- DB(Oemrep) is shutdown


SQL> exit
Disconnected

C:\>sqlplus

SQL*Plus: Release 9.0.1.0.1 - Production on Tue Apr 15 17:13:17 2003

(c) Copyright 2001 Oracle Corporation.  All rights reserved.

Enter user-name: sys as sysdba
Enter password:
Connected to an idle instance.

SQL> select * from global_name;
select * from global_name
*
ERROR at line 1:
ORA-01034: ORACLE not available -- DB(Oemrep) is shutdown


SQL> exit
Disconnected
I used NT (OS) Authentication and also i had 2 instances and no connect string.

Thanks
Abhay.