I would add **$groupby** and **$select** parameters on the REST Web Service invocation URL to apply DISTINCT and to SELECT only the required columns.
The above URL will retrieve and show only the DISTINCT values of *col1*.
You can refer to the [Parameters of the RESTful Web Service](https://community.denodo.com/docs/html/browse/6.0/vdp/administration/restful_architecture/restful_web_service/representations#parameters-of-the-restful-web-service) section of the [Virtual DataPort Administration Guide](https://community.denodo.com/docs/html/browse/6.0/vdp/administration/index) to get more details.
Alternatively, I would perform the following steps:
1. Create a derived view using “**Selection**”, where I keep only the expected column on the **Output** tab and select “**DISTINCT clause**” check box available on the same tab.
1. Publish the newly created derived view as RESTful Web Service to retrieve only the DISTINCT records.
Hope this helps.