When I try to connect to a database, It get an

If you are using multiple Oracle Homes, it is most likely that PL/SQL Developer is using a different Oracle Home than SQL*Plus. By default, PL/SQL Developer will use the Primary Oracle Home (the one that is listed first in the PATH environment variable.

There are 3 ways to resolve this:<OL TYPE=1>
[*] Start PL/SQL Developer, go to Tools > Preferences > Options tab page, and select the correct Oracle Home from the list. Restart PL/SQL Developer and try to connect again.

[*] Use the Oracle Home Selector (a standard Oracle utility) to select a different Primary Oracle Home.

[*] Add the unknown alias through the Oracle Net Configuration Assistant.
</OL>

I have only one Oracle install. But still having problem connect to my database.
What else can I do?

What is your PL/SQL Developer version?

I have a similar problem.

When I try to connect to a remote database with PLSQL Developer, I get the error:

ORA-12154: TNS: could not resolve service name

However, when I use the Oracle Client tool called 'Net Configuration Assistant', it says the test is OK.

I can assert this by catching an ethereal trace in this case, while with PLSQL Developer nothings goes out through the link.

I had a look at this and other similar posts, but nothing seems to work in my case. I can try by deleting the other Oracle client ('oraclient') though it is not the default one.

Anyway, I will gather all the informations for Marco and send you by email.

Well, I have solved the problem...

I have seen with ethereal (without filtering by destination address as I used to do) that it was trying to resolve a name through the DNS servers.

I copy here the service as it is in my tnsnames.ora:

omp =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 159.23.98.26)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = omp)
)
)

Well, the first 'omp' is the name where PLSQLDEVELOPER will try to connect, so it needs to be resolved.

Then, if I add this line to my local hosts file, everything works fine:

159.23.98.26 omp

However, I think this is a bug in the application: in my understanding this name should just be local, to connect to the database server it should use the value:

HOST = 159.23.98.26

Another possible bug is that this name 'omp' has to match exactly the service name, which is actually the one running by the listener in the database server.

To illustrate, if I use those values in tnsnames.ora:

apps =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 159.23.98.26)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = omp)
)
)

and this in hosts:

159.23.98.26 apps

then I get the error ORA-12514.

I am really confused about all this behaviour.