Define Relationships in Azure Analysis Services

Relationships are fundamental to building a functional semantic model in Azure Analysis Services. They define how tables in your model are connected, allowing users to navigate and analyze data across different fact and dimension tables.

Types of Relationships

Azure Analysis Services supports several types of relationships, with the most common being:

• One-to-Many: The most frequent type. A row in one table (the 'one' side, typically a dimension table) corresponds to zero or more rows in another table (the 'many' side, typically a fact table).
• Many-to-Many: Allows for more complex scenarios where multiple rows in one table can relate to multiple rows in another. This often requires an intermediate bridging table.
• One-to-One: Less common, used when two tables have a direct, one-to-one correspondence.

Creating Relationships

You can define relationships using tools like Visual Studio with Analysis Services projects or SQL Server Management Studio (SSMS).

Using Visual Studio

1. Open your Azure Analysis Services tabular model project in Visual Studio.
2. Navigate to the Model Designer.
3. In the diagram view, right-click on the table that will be on the 'many' side of the relationship.
4. Select Create Relationship.
5. In the Create Relationship dialog, select the table and the key column for the 'one' side (typically a dimension table).
6. Select the table and the key column for the 'many' side (typically a fact table).
7. Choose the Cardinality (One-to-Many, Many-to-One, One-to-One, or Many-to-Many).
8. (Optional) Select the Cross Filter Direction.
9. Click OK.

Using SQL Server Management Studio (SSMS)

1. Connect to your Azure Analysis Services instance using SSMS.
2. Navigate to your database and then to the Tables node.
3. Right-click on the table on the 'many' side and select Design.
4. In the table designer, right-click in an empty area and select Relationships.
5. In the Foreign Key Relationships dialog, click Add.
6. Define the primary key table and columns, and the foreign key table and columns.
7. Configure the Insert and Delete Rule as needed (often set to 'No Action').
8. Click OK.

Key Concepts

• Cardinality: Defines the nature of the relationship (one-to-one, one-to-many, etc.).
• Cross Filter Direction: Determines how filters are applied across the relationship. Single direction (default) means filters flow from the 'one' side to the 'many' side. Both directions allow filters to flow both ways.
• Active Relationship: A model can have multiple relationships between tables, but only one can be active for a given pair of tables. The active relationship is used by default for DAX calculations and query processing.