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Database link from Oracle to SQL Server

Oracle Database Tips by Donald Burleson

Question:  How do I create a database link from Oracle to SQL Server.  I need to link to SQL Server as part of a band-aid before migrating everything to Oracle.

Answer:  Oracle heterogeneous services allow you to define a database link between Oracle and SQL Server, as well as links to DB2 and other inferior databases.

Here are complete notes in creating a database link between Oracle and SQL Server.

1. Install Oracle ODBC drivers on the server (your local Oracle database) that will access the remote SQL Server database using the database link.

2. Setup the ODBC connection on the local Oracle database using the Windows ODBC Data Source Administrator

3. Test the ODBC drivers to ensure that connectivity is made to the SQL Server database.

4. Ensure that your global_names parameter is set to False.

5. Configure the Oracle Heterogeneous services by creating an initodbc.ora file within the Oracle database.

7. Modify the Listener.ora file.

SID_NAME is the DSN for the remote database.
ORACLE_HOME is the actual Oracle home file path.
PROGRAM tells Oracle to use heterogeneous services.

(SID_NAME=Cas30C) -- Enter the DSN on this line
(ORACLE_HOME = c:\oracle10gdb) -- Enter your Oracle home on this line
(PROGRAM = hsodbc) ) )


8. Modify the Tnsnames.ora file. This is the Oracle database installation accessed by the users to connect to the ODBC drivers

-- (Server x)
(PORT=1521))) -- Enter the port on which the server x Oracle installation
-- is listening
(CONNECT_DATA=(SID=Cas30c)) - Enter the DSN name
(HS=OK) -- Enter this value. It tells Oracle to use hetergeneous services

9. Reload the listener on local Oracle database

10. Create a database link on the local Oracle installation that accesses the heterogeneous connection, which, in turn, connect to SQL Server.

11. Run a SQL Server Select statement from the Oracle installation using the database link.

If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

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