BI Wizard - Custom Member Formulas for Attributes in a Dimension
Applies to: 
SQL Server Analysis Services 
Azure Analysis Services
Fabric/Power BI Premium
Add a custom member formula enhancement to a cube or dimension to replace the default aggregation that is associated with a dimension member with the results of a Multidimensional Expressions (MDX) expression. (This enhancement sets the CustomRollupColumn property on a specified attribute in a dimension.)
Note
A custom member formula is available only for dimensions that are based on existing data sources. For dimensions that were created without using a data source, you must run the Schema Generation Wizard to create a data source view before adding a custom member formula.
To add a custom member formula, you use the Business Intelligence Wizard, and select the Create a custom member formula option on the Choose Enhancement page. This wizard then guides you through the steps of selecting a dimension to which you want to apply a custom member formula and enabling the custom member formula.
Selecting a Dimension
On the first Create a Custom Member Formula page of the wizard, you specify the dimension to which you want to apply a custom member formula. The custom member formula enhancement added to this selected dimension will result in changes to the dimension. These changes will be inherited by all cubes that include the selected dimension.
Enabling a Custom Member Formula
On the second Create a Custom Member Formula page, you associate the source column that contains the custom member formula with one or more attributes in the dimension. In the Attribute column, select the check box next to the attribute that you want to associate with the custom member formula column. After you select each attribute, the wizard displays the Select a Column dialog box. In this dialog box, click the column in the dimension table that contains the formula. If you want to change a selection after you close the Select a Column dialog box, click the Source Column cell that you want to change, and then click the ellipsis (...) to open the Select a Column dialog box again.