The product and customer dimension views retrieve both the surrogate key column used for relationships in the dataset as well as the business key that uniquely identifies the given product or customer, respectively. For example, the same product (FR-M94B-38) is represented by three product dimension rows (304, 305, 306) due to changes in its list price over time:
Slowly-changing dimension processing applied to Product Dimension
As discussed in Chapter 1, Planning Power BI Projects, the historical tracking of core business entities, such as customers and products, via slowly-changing dimension ETL processes is an essential requirement for data warehouses. The ability to insert and update rows based off of changes in specific columns is well outside the scope of SQL views and M query transformations.
DAX measures will reference the business key or alternate key column of these dimension tables to compute the discount count of these entities. For dimensions without slowly-changing dimension processing applied, the foreign key column of the related fact table can be used to compute the distinct count of dimension values associated with the given fact or event. Greater detail on these measures is included in Chapter 4, Developing DAX Measures and Security Roles.