Something like:
SELECT zzzjunctionTbl.ClassID, zzzjunctionTbl.TeamID, zzzjunctionTbl.EmployeeID,
IIf((Nz([ClassID],0))=0 And (Nz([TeamID],0))=0,[EmployeeID],
IIf((Nz([ClassID],0))>0,[ClassID],
IIf((Nz([TeamID],0)>0),[TeamID],[EmployeeID]))) AS Result
FROM zzzjunctionTbl;
The function NZ is used...