Is it possible? Does the data need to replicated to Azure first and acessed from there? Does code need to be written (i.e. oData Feed or Web Service)?
If you are looking for a no-code solution: Just sync your SQL with a SharePoint Online list one-way or even two-way as described here to make use of the data with NINTEX. No need to open the network for wen services or modify your SQL.
Jeff, we had to create an On Premise oData web service and use a External Content Type and External Data column on the list. You could do the same thing from Azure as well without the oData web service and connect direct to the SQL database I believe from SPD.
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