Hi, Don! I'm entirely the wrong person to answer this since I am not experienced and just created my first mySQL db yesterday and cannot write even a basic SQL query yet, but since no one else has answered yet, I'll throw some stuff out there and maybe it'll help you or someone more capable than I...
Since your 10-day period will be constantly changing and you need to check all employees, what if you create an INT field w/a constant value =1 to represent 1 day worked and and then search for all employees jobs in the past 10 days, sort by employee, and display a sub-summary calculation for each employee that totals the 1 day worked fields?
Sorry I can't SQL-talk yet, but FWIW, that's the logic I might pursue if it were my own project. I don't even know if mySQL has sub-summary calcs but I would think so. Hope this leads to something.