We have few "Database Connections" created in SP Designer 2010 and I used the "Data view" web part to display the database connections' data.
Is it possible to export this data to an excel?
Unfortunately, it's not possible!
Export to Excel option is not available in the
External List in SharePoint 2010. Check the full limitations list at my article External List limitations in SharePoint 2010/2013
Export to Exceloption is available for
External Listin SharePoint 2013.
Unfortunately, there is no OOTB option to export Data View with an external database connection in SharePoint.
But you can use Jquery as a workaround to achieve that as I mentioned at Export Data View to excel in SharePoint