Subtract 2 unrelated character columns in webi ?

Hi

  I have 2 column Product Name and another Model. Both are not related but have almost same data and it is a character field. I need to subtract Product name from Model to see a different column and thus see all the values which are present in column Model and  is not present in Product Name.

I am using BOXI 3.1 Sp3.

I would appreciate if you could help me out here.

Cheers!