My Power BI reports are getting very slow, and I have a "flat table" with 150 columns. I’ve heard that a Star Schema is the best practice. How do I actually break my big table into Fact and Dimension tables, and what are the benefits of using a one-to-many relationship in the model view?
3 answers
A Star Schema is the "Gold Standard" for Power BI. You want one central Fact table containing your quantitative data (sales, quantities, temperatures) and several Dimension tables containing descriptive attributes (products, dates, stores). By using one-to-many relationships from Dimensions to the Fact table, you allow the engine to filter data efficiently. This structure makes your DAX formulas simpler to write and much faster to execute because the engine only has to scan the relevant "slices" of data rather than one massive, wide table.
A Star Schema is the "Gold Standard" for Power BI. You want one central Fact table containing your quantitative data (sales, quantities, temperatures) and several Dimension tables containing descriptive attributes (products, dates, stores). By using one-to-many relationships from Dimensions to the Fact table, you allow the engine to filter data efficiently. This structure makes your DAX formulas simpler to write and much faster to execute because the engine only has to scan the relevant "slices" of data rather than one massive, wide table.
If you have 150 columns, your first step should be deleting the columns you don't actually use in your visuals. Reducing the model width is the fastest way to boost speed.
Great advice, Barbara. Power BI is a columnar database; the fewer columns you have, the better the compression and performance will be.
Be very careful with Bi-directional filters, William! While they seem convenient, they often lead to "circular dependencies" and can cause incorrect totals in your measures. It's much safer to use the CROSSFILTER function in a specific DAX measure when you absolutely need that behavior, rather than turning it on at the model level. Stick to single-direction filtering for a clean, predictable Star Schema.