To start with, I would suggest that you load your [_EMP no] your [EMPhireDate] and your [AMPLeavingDate] into 1 table.
Then make a new field by using:
IF (ISNULL([AMPLeavingDate]) , 'Hired' , "Left' as StatusEMP
Now you have a new field which you can use in your expression or use a selection box in your QV document.
Let me know if this is working for you.