Relationships
Relationships play a central role in the analytical behavior and performance of the dataset. Based on the filters applied at the report layer and the DAX expressions contained in the measures, relationships determine the set of active rows for each table of the model that must be evaluated. Therefore, it’s critical that dataset designers understand how relationships drive report behavior via cross-filtering and the rules that relationships in Power BI must adhere to, such as uniqueness and non ambiguity, as discussed in the next section.
Uniqueness
Relationships in Power BI data models are always defined between single columns in two separate tables. While Power BI does support direct many-to-many relationships, it is recommended that relationships with a cardinality of many-to-many be avoided because this implies that the related columns both contain duplicate values for the related columns. Relationships based on columns containing duplicate values...
