Help with creating a formula

Hi All,

I have 2 columns Column 1 and Column2 and I have derive the Column 3 in webi report based on column 1 and column 2. Please help me how to achieve this by using the BO Functions.

Eg :

Column1    Column2    Column3

1                  A                B

1                  A                B

1                  B                B

2                  C                B 

2                  B                B

3                  D                B

3                  B                B,

Thanks