Build Chart (Score Sheet) that shows all assignments (even missing)

So I have score information for a variety of challenges completed by a number of people. I want to build a chart showing their score information for each challenge individually. Building the chart is easy enough, my problem is that if they haven't completed the challenge (i.e. no score) then the challenge won't show up at all. I have a lookup table with a complete list of the challenges. Is there a way to force all challenges (even the ones without the scores) to show up or to generate or 0 score if the assignment isn't there? Thanks, Troy