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Unfortunately, you can only have one data source in the Visual Report builder.
If I may suggest, perhaps integrating Google Spreadsheet would work for you best? You can integrate your form and submission data on it by following this guide: http://www.jotform.com/help/228-How-to-Integrate-Form-with-Google-Spreadsheet
Google Spreadsheet allows you to use the data and output it in charts. You can have basic to advance charts from there. Merging of multiple fields and outputting it on a proper chart type would also work. You can find the different charts here: https://support.google.com/docs/answer/190718?hl=en. I believe that fits on your case would be a combo chart or something similar to a bar chart.
Let us know if that helps.