What Versions of Microsoft SQL does Nintex support?

Nintex supports all the versions of Microsoft SQL that is supported by the Sharepoint platform

In order to maintain SharePoint and SQL Server compatibility, Microsoft use the “SharePoint N-1 on SQL Server N+1” equation to determine version support.

SharePoint Server 2010 supports  SQL Server is 2008, 2008 R2 and 2012
SharePoint Server 2013 supports  SQL Server is 2008 R2, 2012 and 2014
SharePoint Server 2016 supports  SQL Server is 2014 SP1, 2016 and 2017 RTM