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Why is star schema preferred in Power BI?
From Excel and PowerPoint to Power BI: Why things get messy (and How to Fix It)
Okay, here’s the pain. You’ve been working in Excel for years. You know your way around spreadsheets, pivot tables, even a bit of VLOOKUP magic. You’ve built plenty of tidy reports and nailed your PowerPoint presentations.
- Then someone introduces you to Power BI. You think, “Cool! I’ll just upload my Excel file and design the visuals like I do in PowerPoint.”
- At first, it goes well. The dashboards look flash, and people start noticing. They ask for more, more data, more pages, more filters. You keep adding.
- But suddenly, your report gets slow. It shows the wrong numbers. Filters behave oddly. You feel like something’s broken, but you don’t know what.
- Have you been there? Most of us have.
And in most cases, the problem isn’t your skills, it’s the data model.
And the fix? Star schemas.
Star Schemas: The missing piece in most Power BI Reports
A star schema is a simple way to organise your data so that Power BI runs smoother, faster, and more accurately.
It separates your data into:
- A Fact Table: where the numbers live (sales, revenue, dates)
- Dimension Tables: where the details live (product names, cities, customers)
This structure makes your model lighter, cleaner, and easier to manage, especially as your report grows.
Flat Tables vs. Star Schemas
| Feature | Flat Table Model | Star Schema Model |
|---|---|---|
| Data Structure | Single table with repeated information | Central fact table + linked dimensions |
| File Size | Larger due to data duplication | Smaller and more efficient |
| Performance | Slower as data grows | Optimised for large volumes |
| Ease of Maintenance | Hard to update and debug | Easier to manage and expand |
| DAX Formulas | Can become messy and long | Simpler and more reusable |
| Best For | Small files or quick one-off reports | Scalable, long-term dashboards |
When Star Schemas make the biggest impact
| Scenario | Flat Table Risk | Star Schema Benefit |
|---|---|---|
| Dashboard grows from 1 sheet to 10+ | Model slows down | Cleaner structure keeps speed high |
| Adding filters like customer, region | Filters break or double count | Filters work accurately |
| Reusing logic across visuals | Hard to manage in one table | Dimensions keep logic reusable |
| Multiple report authors involved | Errors and duplication | Clear separation improves collaboration |
We built a tool to help You learn and use Star Schemas
To make things easier, we built a free Python-based tool at Excel in BI that helps you:
- Upload an Excel or CSV file
- Choose which columns become Dimensions
- Create a proper Fact Table
- Automatically generate surrogate keys
- Export everything into Excel or Parquet files, ready for Power BI
It’s simple, visual, and helps you see the benefits straight away.
Ready to give it a go?
Sign up to download the tool, receive a free guide on Star Schemas from Excel in BI, and get an invitation to our next live webinar.
We’ll show you how to structure your data, avoid common Power BI headaches, and make reports that people trust, and actually use.
