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Power BIbi_tool~5 mins

Why data modeling connects related tables in Power BI - Why Use It

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Introduction
Data modeling in Power BI links tables that share common information. This connection helps combine data from different tables to create meaningful reports and insights without repeating data.
When you have sales data in one table and customer details in another, and you want to analyze sales by customer region.
When product information is stored separately from sales transactions, and you want to see total sales per product category.
When you want to filter data in one table based on selections made in another table, like filtering orders by date.
When you need to create reports that summarize data from multiple tables without merging them into one big table.
When you want to avoid data duplication and keep your data organized and efficient.
Steps
Step 1: Open your Power BI Desktop file
- Power BI Desktop main window
Your data tables are loaded and visible in the Fields pane
Step 2: Click the Model view icon
- Left vertical pane (Model icon)
You see all your tables as boxes with columns listed
Step 3: Drag a column from one table to the matching column in another table
- Model view canvas
A relationship line appears connecting the two tables
Step 4: Select the relationship line
- Model view canvas
Relationship settings pane opens on the right
Step 5: Check and adjust the relationship type and cardinality
- Relationship settings pane
Relationship is correctly set as one-to-many or many-to-one, ensuring accurate data connection
💡 Use one-to-many when one table has unique values and the other has repeated values
Step 6: Close the settings pane and return to Report view
- Top left corner, click Report icon
You can now create visuals that use data from both connected tables
Before vs After
Before
Tables are separate with no connections; creating a report combining customer names and sales amounts shows incorrect or incomplete data
After
Tables are connected by customer ID; reports correctly show sales amounts linked to each customer name
Settings Reference
Cardinality
📍 Relationship settings pane in Model view
Defines how rows in one table relate to rows in another table
Default: One to many
Cross filter direction
📍 Relationship settings pane in Model view
Controls how filters flow between related tables
Default: Single
Make this relationship active
📍 Relationship settings pane in Model view
Determines if the relationship is used by default in calculations
Default: Checked
Common Mistakes
Connecting tables using columns that do not have matching or unique values
This causes incorrect relationships and wrong report results
Always connect tables using columns with matching data and unique values on one side
Setting cross filter direction to Both without understanding its impact
It can cause ambiguous relationships and slow report performance
Use Single direction unless you need filters to flow both ways
Summary
Data modeling connects tables to combine related information for accurate reports.
Relationships use matching columns to link tables without merging data.
Correct relationship settings ensure data filters and calculations work properly.