Can I speed up the search for people who successfully completed a course?

Summary:

I need to generate a list of who's completed a specific course. I don't care how often they've completed it - I just need to know if they've got at least one successful completion record.

Content (please ensure you mask any confidential information):

It's easy to generate a list of who's successfully completed the course by searching for people whose completion date is not NULL. However, that generates duplicate entries and there are over 4,000 people who need to pass this course every year.

Is there a way to tell the analysis to move on to the next user as soon as it finds the first instance of the current user?