I'm not sure if I understood your requirement.
Do you want to filter the sales of 2011 but show all staff? They would have 0 as result, right?
If I got it, then you don't need to change the expressions, but only the chart settings.
You need to uncheck the 'supress zeros' on the presentation tab.
You may also have to check the show all values on the dimensions tab.
Please, check my attachment.
KEEP DIMENSIONS ON AXIS.qvw 135.2 K