Struggling to get a SQL DataConnector working

[Rod Widdowson]

>             <![CDATA[
>                 SELECT *
> 				FROM dbo.Staging
> 				WHERE username =
> '${requestContext.principalName}'
>             ]]>

I'm pretty sure you don't want the braces.  Also this is V2 legacy syntax,
you might be better with 

SELECT * FROM dbo.Staging WHERE username='$resolutionContext.principal'

Rod