The answer is to split columns that contain multiple values into separate rows and promote headers. Splitting columns with multiple values into separate rows is a best practice because it normalizes your data structure, ensuring each row represents a single, atomic value—this is critical for accurate aggregations and relationships in Power BI’s data model. Promoting headers is equally essential because it tells Power Query to treat the first row of your source data as column names, preventing those values from being misread as data entries, which would break field references and measures. On the PL-300 exam, these two transformations frequently appear together in scenario-based questions, often testing your ability to recognize when raw data requires unpivoting or header promotion before loading. A common trap is assuming that splitting columns into new columns (instead of rows) is sufficient, but the exam emphasizes row-level normalization for proper filtering and DAX calculations. Remember the mnemonic: “Split to rows, promote the rows” to recall that both actions clean structure and metadata for a reliable 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.
Which TWO are best practices when preparing data for Power BI?
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
✓
Promote headers if the first row contains column names
Option B is correct because promoting headers is a best practice when the first row of your source data contains column names. This ensures that Power BI correctly interprets those values as field names rather than data, which is essential for accurate data modeling and reporting. The 'Promote Headers' transformation is a standard step in Power Query to clean and structure imported data.
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.
✗
Change data type of all columns after all transformations
Why it's wrong here
Should be done early to avoid errors.
✓
Promote headers if the first row contains column names
Why this is correct
Ensures proper column names.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Split columns that contain multiple values into separate rows
Why this is correct
Normalizes data.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Avoid merging queries; always use lookups
Why it's wrong here
Merging is a valid transformation.
✗
Avoid unpivoting columns; keep data wide
Why it's wrong here
Unpivoting often needed for analysis.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think changing data types at the end is safer (Option A) or that merging queries should be avoided (Option D), but the exam tests understanding that data type changes should be applied early and that merging is a standard relational data preparation technique.
Detailed technical explanation
How to think about this question
In Power Query, the 'Promote Headers' operation uses the first row of the table to rename the columns, which is stored as metadata in the M language. This step is critical when importing data from sources like Excel or CSV where headers are not automatically recognized. A common subtle behavior is that if the first row contains null or duplicate values, Power Query will generate default column names (e.g., Column1, Column2), which can break downstream transformations if not handled.
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: Promote headers if the first row contains column names — Option B is correct because promoting headers is a best practice when the first row of your source data contains column names. This ensures that Power BI correctly interprets those values as field names rather than data, which is essential for accurate data modeling and reporting. The 'Promote Headers' transformation is a standard step in Power Query to clean and structure imported data.
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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