The database of multi-tenant Software as a Service (SaaS) applications has challenges in designing and developing a relational database for multi-tenant applications. In addition, combining relational tables and virtual relational tables to make them work together and act as one database for each single tenant is a hard and complex problem to solve. Based on our multi-tenant Elastic Extension Tables (EET), we are proposing in this paper a multi-tenant database proxy service to combine multi-tenant relational tables and virtual relational tables, to make them act as one database for each single tenant. This combined database is suitable to run with multi-tenant SaaS single instance applications, which allow tenants designing their database and automatically configuring its behavior during application runtime execution. In addition, these applications allow retrieving tenants data by simply calling functions from this service which spare tenants from spending money and efforts on writing SQL queries and backend data management codes, and instead allowing them to focus on their business and to create their web, mobile, and desktop applications. The feasibility and effectiveness of the proposed service are verified by using experimental data on some of this service functions.