The answer is to remove unused columns from the table in Power Query. This is correct because every unnecessary column adds substantial I/O and memory overhead during the import process, especially with a 10 million row dataset; by stripping out these columns before the data is loaded, you directly reduce the volume of data transferred and processed, which is the most effective way to improve power bi import refresh performance. On the Microsoft Power BI Data Analyst PL-300 exam, this scenario tests your understanding of data shaping in Power Query as a foundational optimization technique—a common trap is to assume that adding indexes or changing the storage mode is the fix, but the simplest and most impactful step is to eliminate columns that aren’t used in reports or the model. Remember the memory tip: “If it’s not in the view, don’t let it through”—every column you keep is a column Power BI must refresh.
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.
A company has a Power BI dataset that imports data from a SQL Server database. The dataset includes a table with 10 million rows. The data model uses a single table and does not include any calculated columns or measures. The report users report that the dataset refresh takes too long. Which action should you take to improve refresh performance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove unused columns from the table in Power Query.
Removing unused columns from the table in Power Query reduces the amount of data loaded into the Power BI dataset. With 10 million rows, every unnecessary column adds significant I/O and memory overhead during refresh. This directly improves refresh performance by minimizing the data volume transferred and processed.
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.
✗
Increase the scheduled refresh frequency to every 15 minutes.
Why it's wrong here
Increasing frequency does not reduce refresh time.
✗
Enable Query Folding on all steps in Power Query.
Why it's wrong here
Query Folding is already enabled by default; no steps are defined.
✗
Change the storage mode to DirectQuery.
Why it's wrong here
DirectQuery may reduce refresh time but changes query behavior and may not be suitable.
✓
Remove unused columns from the table in Power Query.
Why this is correct
Reduces data volume and improves refresh speed.
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 often confuse refresh performance with query performance, leading them to choose DirectQuery (Option C) which solves query latency but does not improve the import refresh time that the question explicitly targets.
Detailed technical explanation
How to think about this question
Under the hood, Power BI's VertiPaq engine compresses imported data column by column. Removing unused columns reduces the dictionary size and column segments, leading to faster data loading and lower memory consumption. In real-world scenarios, a table with 10 million rows and 50 columns might have 20 columns never used in reports; removing them can cut refresh time by 30-50% because fewer column scans and compression operations are needed.
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: Remove unused columns from the table in Power Query. — Removing unused columns from the table in Power Query reduces the amount of data loaded into the Power BI dataset. With 10 million rows, every unnecessary column adds significant I/O and memory overhead during refresh. This directly improves refresh performance by minimizing the data volume transferred and processed.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A Power BI dataset is configured to use Import storage mode. The dataset includes a fact table with 100 million rows and several dimension tables. The report is slow when users interact with visuals. You need to improve query performance without changing the storage mode. Which action should you take?
medium
✓ A.Create aggregations on the fact table.
B.Increase the scheduled refresh frequency.
C.Reduce the number of dimension tables.
D.Enable 'Load to report' for all tables.
Why A: Creating aggregations on the fact table allows Power BI to pre-summarize data at higher granularity levels, reducing the amount of data scanned during query execution. Since the dataset uses Import mode, aggregations leverage the in-memory columnar storage to serve queries from pre-computed tables, significantly improving visual response times without altering the storage mode.
Last reviewed: Jun 11, 2026
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This PL-300 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PL-300 exam.
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