It's not possible to show or hide the columns of an expression if they is below of any dimension and returned at least a single result for any cell-value.
A workaround for you could be to add those 'Total' as an additionally field-value to your Dim1 (it could be done with a small concatenate-statement from an inline-table) and then to query this value within the expression. Another way is to add another (maybe artificial) dimension above Dim1 - if none native exists it might be just a calculate dimension with a string like 'all Dim1 value' - and then you could query the dimensionality, for example like:
if(secondarydimensionality() = 0, ExprDato2, ExprDato1)
- Marcus
