In Oracle, how do you change the 'default' database? - linux

Question

I really should know this, but would someone tell me how to change the default database on Linux?
For example:
I have a database test1 on server1 with ORACLE_SID=test1. So, to connect to test1 I can use:
sqlplus myuser/password
Connects to the default database, test1
I would now like the default sqlplus connection to go to database test2 on server server2.
So, I've updated tnsnames so that the old test1 entry now points to test2#server2. I've also added a separate entry for test2 that points to the same place. However, the default connection still seems to go to test1#server1.
The following both work fine and go to database test2 on server2:
sqlplus myuser/password#test1
sqlplus myuser/password#test2
But the default connection, sqlplus myuser/password, goes to test1#server1.
Any ideas?
Thanks.

Answer 1

To expand on kerchingo's answer: Oracle has multiple ways to identify a database.
The best way -- the one that you should always use -- is USER/PASSWORD#SERVER. This will use the Oracle naming lookup (tnsnames.ora) to find the actual server, which might be on a different physical host every time you connect to it. You can also specify an Oracle connection string as SERVER, but pretend you can't.
There are also two ways to specify a default server via environment variables. The first is TWO_TASK, which uses the naming lookup, and the second is ORACLE_SID, which assumes that the server is running on the current machine. ORACLE_SID takes precedence over TWO_TASK.
The reason that you should always use an explicit connect string is that you have no idea whether the user has set TWO_TASK, ORACLE_SID, both, or neither; nor do you know what they might be set to. Setting both to different values is a particularly painful problem to diagnose, particularly over the phone with a person who doesn't really understand how Oracle works (been there, done that).

Answer 2

Assuming you're logged into server1, you'll need to connect to test2 using
sqlplus myuser/password#test2
because you have to go through a listener to get to server2. The string test2 identifies an entry in your tnsnames.ora file that specifies how to connect to test2. You won't be able to connect to a different server using the first form of your sqlplus command.
If both instances (test1, test2) were on server1, then you could, as #kerchingo states, set the ORACLE_SID environment variable to point at another instance.

Answer 3

Defining a enviroment variable LOCAL with the tns alias of your database.
> set LOCAL=test1
> sqlplus myuser/password
> ... connected to test1
> set LOCAL=test2
> sqlplus myuser/password
> ... connected to test2
This works on windows client, not shure about other os.

Answer 4

The correct question is 'How do I change the default service'? Oracle DBMS offers two types of connection request: explicit and implicit. In an explicit request, you supply three operands like sqlplus username/password#service. In an implicit request, you ignore the third operand.
Implicit connection applies only when the client-host and server-host are the same. Consequently, the listener is on the same host.
The listener is the one that initially responds to connection request. In handling the implicit-connection request from the same host,
it checks whether the instance name has been set. It checks the value of shell-variable ORACLE_SID.
If set, then it can handle implicit-connection request. Otherwise, it cannot, and you must perform explicit-connection request, supplying the third operand.
The listener-config file name listener.ora associates instance with service.
To change the default service you connect to, change the default value of instance.
Therefore, change the default value of shell-variable ORACLE_SID. You do it in the OS user config file such as .profile or similar config files.
Hope this helps.

Answer 5

I think it is set in your environment, can you echo $ORACLE_SID?