PL-300 Prepare the data Practice Question
You are building a Power BI data model with multiple fact tables and dimension tables. One of the dimension tables has a one-to-many relationship with two fact tables, but the relationships are inactive. You need to create measures that use both fact tables and the dimension table without relying on user interactions to activate relationships. What should you do?
⚠ Common exam trap
Many exam-takers think they must make all relationships active or merge tables to use a dimension with multiple fact tables, not realizing that USERELATIONSHIP provides a clean, dynamic solution without compromising model integrity.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the USERELATIONSHIP function in the measure definition.
The USERELATIONSHIP function in DAX allows you to temporarily activate an inactive relationship within a measure definition. This enables you to use a dimension table with multiple fact tables without changing the model's default active relationships or relying on user interactions. By specifying the inactive relationship in the measure, you can perform accurate aggregations across both fact tables while maintaining the intended data model structure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Merge the fact tables into one table.
Why it's wrong here
Merging the fact tables into one would change the grain of the data, causing row duplication or loss of detail because each fact table typically records events at different levels. This violates star schema best practices and makes it impossible to maintain separate relationships to shared dimensions. The result is inaccurate aggregations and a model that is hard to maintain.
- ✗
Create calculated columns in the dimension table to relate to each fact table.
Why it's wrong here
Calculated columns in a dimension table cannot enforce relationships because they are just static values computed at refresh time and do not create relational integrity between tables. To filter one table by another, you need a physical model relationship, not a mere column match. Additionally, calculated columns consume memory and storage, and they would not resolve the problem of having two active relationships.
- ✓
Use the USERELATIONSHIP function in the measure definition.
Why this is correct
USERELATIONSHIP is the DAX function designed to activate a specific inactive relationship inside a measure definition by taking two column arguments. It temporarily overrides the default active relationship for that measure only, leaving the model's active relationship intact for all other calculations. This is the standard pattern for handling multiple paths between the same tables, such as Order Date and Ship Date both referencing a Calendar table.
- ✗
Change both relationships to active.
Why it's wrong here
Power BI allows only one active relationship between any two tables; attempting to set both as active would either be rejected by the engine or produce ambiguous filter propagation across measures. If both were active, every measure would require explicit relationship specification, eliminating the benefit of a default filter path. The correct practice is to keep one relationship active for standard filtering and mark the other as inactive, then use USERELATIONSHIP when that alternate relationship is needed.
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