Did you try sort option on that col? if yes what you are getting?
Use the number key column to sort this column if you have any, I dont think OBIEE has ability to sort character's
Mark points, If it helps
The column is varchar2 datatype..So,it sorted like
Adding to Srix: Not only obiee any tool not able to sort as you required.
Assuming Emp no are sequentially except contract employees, I would suggest sort on created date of employee record that would help you to get some order and all alphanumeric once at the end.
just in case if you get any sol let me know