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 are reviewing a Power Query query that combines data from multiple CSV files in a folder. The query uses the 'Combine Files' function. Which TWO actions can you take to improve the performance of this query?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Disable the 'Promote Headers' step if the headers are not needed.
Option B is correct because disabling the 'Promote Headers' step reduces the number of transformations applied to each file during the combine operation. When headers are not needed, skipping this step avoids an extra row promotion and type detection pass, which can significantly reduce query execution time, especially when combining many files.
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.
✗
Load all data to the data model without filtering.
Why it's wrong here
Increases load time.
✓
Disable the 'Promote Headers' step if the headers are not needed.
Why this is correct
Avoids unnecessary processing.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the scheduled refresh frequency.
Why it's wrong here
Does not improve query performance.
✓
Filter the folder to include only relevant files before combining.
Why this is correct
Reduces the number of files to process.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable 'Fast Combine' in the Power Query options.
Why it's wrong here
Privacy setting, not performance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Microsoft often tests the misconception that increasing refresh frequency or enabling privacy-level settings like 'Fast Combine' improves query performance, when in fact they address different concerns (scheduling and data privacy, respectively).
Detailed technical explanation
How to think about this question
The 'Combine Files' function in Power Query uses a sample file to infer schema and then applies the same transformations to all other files. Disabling 'Promote Headers' avoids an extra Table.PromoteHeaders call per file, which is particularly beneficial when dealing with hundreds of files where each promotion adds overhead. In real-world scenarios, if the CSV files already have consistent headers, you can also use 'Use First Row as Headers' only once on the sample file, then skip the promotion step for the remaining files.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: Disable the 'Promote Headers' step if the headers are not needed. — Option B is correct because disabling the 'Promote Headers' step reduces the number of transformations applied to each file during the combine operation. When headers are not needed, skipping this step avoids an extra row promotion and type detection pass, which can significantly reduce query execution time, especially when combining many files.
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.
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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