Power pivot creating a relationship with columns with duplicate values

Question

I am creating my first Power Pivot.  I have two excel imports related to payroll.  Both have employee numbers referenced and one has employee names so I wanted to create a relationship.  These exports cover the entire year thus there are duplicate rows for each employee based upon the pay period.  When I try to create a relations ship I get the error that relationship cannot be created because each column contains duplicate values.  Select at least one column that contains only unique values....I will later create a pivot table that gives me total payroll by employee etc.   What am I doing wrong...