Demystifying Denormalisation in Power BI

This guide will explain how to use denormalisation in Power BI effectively.

Learning how to denormalise data in Power BI can significantly improve the performance of your reports and simplify the data model. By mastering this technique, you'll be able to create faster, more efficient dashboards that provide valuable insights for decision-making.

Unfortunately, many people don't know how to denormalise data in Power BI properly or are unaware of its benefits.

Lack of familiarity with the concept is the primary reason why. Other reasons people struggle with denormalisation in Power BI include the following:

• Struggle #1: Insufficient knowledge of database structures and relationships
• Struggle #2: Fear of data integrity loss
• Struggle #3: Inadequate understanding of Power BI's data transformation capabilities
• Struggle #4: Not knowing when to denormalise data and when to leave it normalised

But don't worry! We will guide you through overcoming these challenges and successfully implementing denormalisation in Power BI.

Here's how step by step:

Step 1: Understand the fundamentals of denormalisation

It's crucial to grasp the concept of denormalisation and its implications on data modelling and those within Power BI.

Denormalisation combines multiple related tables in a data source into a single table to optimise read performance and simplify queries. The trade-off here is increased storage space and reduced data consistency, as redundant data can be introduced. Denormalisation is typically employed when a use case prioritises read-heavy operations over write-heavy operations - usually when building Power BI reports.

Take the time to learn about the differences between normalisation and denormalisation and their trade-offs. First, familiarise yourself with star and snowflake schemas, as these are common database structures used in denormalised models. Then, study how denormalisation can lead to improved query performance and reduced complexity in Power BI.

Step 2: Assess your data model and determine if denormalisation is necessary

A common mistake is denormalising data indiscriminately without considering whether it's appropriate for the specific use case.

Analyse your data model and identify tables with one-to-one or one-to-many relationships that could benefit from denormalisation. Consider factors such as query performance, data volume, and the complexity of your model.

Remember that denormalisation may not always be the best choice and may not be necessary, so weigh the pros and cons before deciding.

Step 3: Implement denormalisation in Power BI using Power Query

Now that you have a solid understanding of denormalisation and have identified potential areas for improvement, it's time to put it into practice.

Use Power Query to merge and consolidate tables, create calculated columns, and apply any necessary transformations.

Test your denormalised data model, ensuring it delivers the expected performance improvements and simplifications.

This article can't cover the ground needed to understand denormalisation and its trade-offs, so go forth and learn more and add another tool to your Power BI arsenal - I can guarantee you not a lot of developers are doing this.