Microsoft Power BI Complete Reference

Declaring the grain

All rows of a fact table should represent the individual business process from step 1 at a certain level of detail or grain such as the header level or line level of a purchase order. Therefore, each row should have the same meaning and thus contain values for the same key columns to dimensions and the same numeric columns.

The grain of fact tables ultimately governs the level of detail available for analytical queries as well as the amount of data to be accessed:

• Determine what each row of the different business processes will represent:
  • For example, each row of the Internet Sales fact table represents the line of a sales order from a customer
  • The rows of the Sales and Margin Plan, however, are aggregated to the level ...