1. Download the jTDS 3rd party JDBC driver, version 1.2.8 from here https://sourceforge.net/projects/jtds/files/jtds/1.2.8/jtds-1.2.8-dist.zip/download
2. Save and extract the contents of the jtds-1.2.8-dist.zip file somewhere safe (ex: “C:oraclesqldeveloperadd-onsjtds-1.2.8-dist”).
3. Start SQL Developer go to Tools > Preferences > Database > Third Party JDBC Drivers.
4. Click “Add Entry”, point to the ‘jtds-1.2.8.jar’ file location, then select it and click OK.
5. Create a new connection, and choose the “SQLServer” tab.
6. Enter the following details: Connection Name (required for database retrieval), Username, Password, Hostname, and Port.
7. Click “Retrieve database” and select the appropriate database, then Save/Test/Connect as you would do normally.