👥 What Is a Relationship in Power BI?

A relationship informs Power BI how tables are connected, typically through a shared column such as CustomerID, ProductID, or Date.

Without these relationships, Power BI cannot match data between tables, leading to blank entries or inaccurate totals in your reports.

🔄 The 3 Types of Relationships

1. One-to-One (1:1)
Rare but useful when both tables contain unique values.
For example, the Employee table and the EmployeeDetails table.

2. One-to-Many (1:*)
The most common type of relationship.
For example, one product can have many sales.

3. Many-to-Many (:)

Challenging to manage.
For example, sales territories with multiple representatives in each region.

🛠️ How to Build a Relationship
Open Model view.
Drag a column from one table to the corresponding column in another table.
Select the appropriate cardinality (1:1, 1:*, etc.).
Choose a filter direction (typically single).
Now, the tables are connected.

⚠️ Factors That Break Relationships

Lack of unique values on one side (Power BI requires this).
Ambiguous filter paths.
Relationships established in the wrong direction.
Failing to create a relationship altogether 😅.

✅ Pro Tips
Maintain clean and unique lookup tables (Customers, Products, Dates).
Avoid circular relationships.
Always review your model diagram—it serves as your map 🗺️.
Test relationships using simple visuals, such as slicers.