The answer is to apply a filter in Power Query before loading. This is the best practice to reduce data loaded in Power Query because it leverages query folding, where Power Query translates your filter into OData query parameters like $filter, pushing the data reduction upstream to the source server. By filtering early, you minimize network transfer and memory consumption in the data model, directly supporting the principle of early filtering in the ETL process. On the Microsoft Power BI Data Analyst PL-300 exam, this concept tests your understanding of query folding and source-side optimization—a common trap is filtering after loading or using Power BI visuals to limit data, which still loads the full dataset. Remember the memory tip: “Filter first, fold fast”—if you see an OData or SQL source, always apply row-level filters in Power Query to ensure only necessary data enters the model.
PL-300 Prepare the data Practice Question
This PL-300 practice question tests your understanding of prepare the data. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You have a Power Query query that loads data from an OData source. You need to reduce the amount of data loaded into the data model. What is the best practice?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Apply a filter in Power Query before loading.
Option C is correct because applying filters in Power Query before loading data into the data model is the best practice for reducing data volume. Power Query pushes filters down to the OData source using OData query parameters (e.g., $filter), ensuring only the required rows are retrieved from the source. This minimizes network transfer and memory usage in the data model, aligning with the principle of early filtering in the ETL process.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Apply a filter in the data model using DAX.
Why it's wrong here
DAX filters are applied after data is loaded, so they don't reduce data volume.
✗
Use 'Enable load' option to turn off loading for the query.
Why it's wrong here
That prevents loading entirely, but if you need some data, it's not appropriate.
✓
Apply a filter in Power Query before loading.
Why this is correct
Filtering in Power Query reduces the amount of data loaded into the model.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Load all data and then hide columns you don't need.
Why it's wrong here
Hiding columns doesn't reduce data volume; it just hides them from report consumers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse filtering in the data model (DAX) with filtering during data ingestion (Power Query), assuming both reduce data volume equally, but only Power Query filters reduce the actual data loaded into memory.
Detailed technical explanation
How to think about this question
When connecting to an OData source, Power Query translates filter steps into OData system query options like $filter, $select, and $top, which are executed server-side. This query folding ensures that only the filtered rows are transferred over the network, significantly reducing load times and memory footprint. In contrast, applying filters after loading (e.g., in DAX) forces Power BI to store the entire dataset, which can lead to performance degradation in large datasets.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Prepare the data — This question tests Prepare the data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Apply a filter in Power Query before loading. — Option C is correct because applying filters in Power Query before loading data into the data model is the best practice for reducing data volume. Power Query pushes filters down to the OData source using OData query parameters (e.g., $filter), ensuring only the required rows are retrieved from the source. This minimizes network transfer and memory usage in the data model, aligning with the principle of early filtering in the ETL process.
What should I do if I get this PL-300 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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