If I assume that you want this calculation to be attached to the rest of your application I suggest adding a new field in your original table and adding a new table based on that new fiekd value. I'll explain.
[Column A] & '|' & [Column B] as [%ColumnKeyAB]
Drop table Original;
Subfield(%ColumnKeyAB,'|') as [Column AB]
Then use Column AB as your dimension for your calculation.