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.
Which THREE of the following are best practices when preparing data in Power BI for optimal performance?
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
✓
Set correct data types for all columns.
Setting correct data types for all columns (Option C) is a best practice because it ensures that Power BI uses the most efficient storage and processing methods. Incorrect data types can lead to increased memory usage, slower query performance, and inaccurate calculations, as Power BI must perform implicit conversions at query time.
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.
✗
Merge all tables into a single table for simplicity.
Why it's wrong here
Merging can lead to denormalization and larger model.
✗
Create calculated columns instead of measures when possible.
Why it's wrong here
Calculated columns increase model size.
✓
Set correct data types for all columns.
Why this is correct
Proper data types improve storage and performance.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Remove unnecessary columns and rows during import.
Why this is correct
Reduces model size and improves performance.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use query folding to push transformations to the data source.
Why this is correct
Reduces data transfer and leverages source performance.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think merging all tables simplifies the model (Option A) or that calculated columns are more efficient than measures (Option B), but Power BI's in-memory engine and query folding mechanics reward normalized star schemas and measure-based calculations for optimal performance.
Detailed technical explanation
How to think about this question
Under the hood, Power BI's VertiPaq engine uses columnar compression, and setting correct data types (e.g., using Integer instead of String for numeric IDs) allows for better dictionary encoding and run-length encoding. For example, a Date column stored as Text will not benefit from date-specific optimizations like automatic time intelligence, and will consume more memory. In real-world scenarios, a column with mixed data types (e.g., numbers stored as text) can break query folding, forcing transformations to occur in Power Query instead of the source database, which degrades performance.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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: Set correct data types for all columns. — Setting correct data types for all columns (Option C) is a best practice because it ensures that Power BI uses the most efficient storage and processing methods. Incorrect data types can lead to increased memory usage, slower query performance, and inaccurate calculations, as Power BI must perform implicit conversions at query time.
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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