PL-300 Model the data Practice Question
A Power BI developer needs to model data from two sources: an on-premises SQL Server database and a cloud-based Salesforce instance. The developer wants to create a star schema in Power BI. Which approach should the developer use to combine the data?
⚠ Common exam trap
Test-takers frequently think a composite model (Option D) is the best approach for combining on-premises and cloud sources, but the question specifically asks for creating a star schema, which is most easily achieved by importing all data into a single in-memory model using Power Query, avoiding the limitations and complexity of mixed storage modes.
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 Power Query in Power BI Desktop to import both sources and merge/append queries as needed.
Power Query in Power BI Desktop is the appropriate tool to import data from both an on-premises SQL Server database and a cloud-based Salesforce instance, allowing the developer to merge or append queries as needed to shape the data into a star schema. This approach supports combining disparate sources into a single import model, which is essential for creating a star schema with fact and dimension tables. Using Power Query ensures that all data is loaded into memory, enabling fast query performance and full modeling capabilities.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use DirectQuery for both sources and create relationships in the model.
Why it's wrong here
Selecting DirectQuery for both the on-premises SQL Server and Salesforce keeps all data in the source systems, which eliminates Power Query's ability to merge or append tables from different sources before loading. Without that shared, shaped layer, you can only relate separate DirectQuery tables via model relationships, which severely limits building a star schema with unified dimension tables, especially when keys or fields require cleansing and combining. DirectQuery also pushes query execution to the source databases for every visual interaction, causing performance bottlenecks on both on-premises and cloud systems.
- ✓
Use Power Query in Power BI Desktop to import both sources and merge/append queries as needed.
Why this is correct
Power Query in Power BI Desktop allows importing data from both on-premises SQL Server and cloud-based Salesforce, enabling merging/append operations to shape data into a star schema. This in-memory model supports all relationships and calculations needed.
- ✗
Use Power BI dataflows to ingest both sources and then reference them in a dataset.
Why it's wrong here
Using Power BI dataflows to ingest sources is suitable for centralising data preparation and ensuring consistency across multiple datasets, handling both on-premises SQL Server (via a gateway) and Salesforce. However, dataflows provide the prepared tables; they do not *create* the star schema or define relationships within the Power BI dataset itself. The modelling, including establishing the star schema and its relationships, occurs within Power BI Desktop after the dataflows have provided the source entities. Dataflows are excellent for enterprise-wide data preparation, but the star schema construction is a subsequent step within the dataset.
- ✗
Create a composite model using DirectQuery for SQL Server and Import for Salesforce.
Why it's wrong here
This option fails because creating a unified star schema often necessitates extensive data transformation, merging, and shaping in Power Query, which is fully supported only when all data is in Import mode. DirectQuery tables cannot be directly merged or appended with Import tables within Power Query to form a cohesive star schema. However, a composite model is appropriate when relating separate tables from different storage modes, allowing real-time DirectQuery data to coexist with imported data in the same model.
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