I understand that I need to configure database address in the TNSNAMES.ORA file but where should I put this file?


I defined the $TNS_ADMIN variable, created the TNSNAMES.ORA file, added new connection and restarted my machine. Unfortunately, the Database list in Oracle Logon remains empty.

However, the following error occurred when I was trying out various options in PL/SQL Developer:

Initialization error
SQL*Net not properly installed


What is SQL*Net?

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You need to have SQL*Net installed in order to connect PL/SQL Dev to Oracle. SQL*Net is installed by default with most Oracle DB products (Oracle client for example). Since PL/SQL dev is a Windows app, you can see what Oracle products you have installed by looking into the registry (HKEY_LOCAL_MACHINE\SOFTWARE\Oracle). Also in PL/SQL dev settings (Tools/Preferences/Connection) you will have a list of all Oracle Homes (which allows you to specify which one you want to use if you have multiple homes).

If you already have an Oracle Home, the TNSNAMES.ora file is by default in the directory %ORACLE_HOME%\network\admin. You can set the registry key TNS_ADMIN if you want to specify another directory.

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  • I have no HKEY_LOCAL_MACHINE\SOFTWARE\Oracle key. I tried to download Oracle client from oracle.com/technetwork/topics/winsoft-085727.html and got the instantclient-basic-nt- file. How should I install it so it creates appropriate registry keys? – Marek Grzenkowicz Apr 15 '11 at 12:29
  • @Marek: I have little experience with the Instant Client. From the FAQ it looks like some features require that you define an ORACLE_HOME system variable. The link also indicates how you could setup instantclient in the registry. I don't know if this would work with Pl/sql Developer (I've always used the Oracle full client). – Vincent Malgrat Apr 15 '11 at 12:49
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    @Marek: There is standalone client installation. Oracle Database 11g Release 2 Client ( for Microsoft Windows (32-bit) - otn.oracle.com. During "Seclect Installation Type" choose "Administrator" and that's it. You can download/install/try anything from OTN, just make sure that you have correct license when go production. – Štefan Oravec Apr 16 '11 at 8:35

I wrote an article way back when I was working with Oracle 10g about trying to connect to a database from a client with too many clients installed on it.

It does go through some basics though so you might want to have a look.


Otherwise yeah. Go for the full client rather than the instant client. I remember having a hard time getting it to work but since then it might have gotten better.

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First close the window and then under Tool->Preferences->Oracle->Connection fill the following fields:

  • Oracle Home (empty is autodetect): C:\oracle
  • OCI library (empty is autodetect): C:\oracle\bin\oci.dll
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