This article explains how to connect Amazon RDS Custom for Oracle to SQL Server using Oracle Database Gateway, enabling cross-database queries and data integration in heterogeneous environments.

• RDS Custom for Oracle comes preinstalled with Oracle database gateway software
• Install MSSQL ODBC Driver on the RDS Custom for Oracle instance
• Configure ODBC Gateway files: odbcinst.ini and odbc.ini for SQL Server connection
• Test connectivity using sqlcmd or isql utilities before proceeding
• Create database link in Oracle referencing configured ODBC data source
• Configure Oracle Heterogeneous Service files: initMSSQL.ora, tnsnames.ora, listener.ora
• Implement security best practices: encryption, strong authentication, access control, audit trails
• Monitor performance and optimize SQL statements for efficiency
• Note: RDS Custom for Oracle support ends March 31, 2027; migrate to EC2 recommended

This solution enables seamless integration between Oracle and SQL Server databases, allowing organizations to leverage both platforms' strengths for improved data analysis and operational efficiency.