Quick Answer
The answer is Pivot columns and adding a custom column with a complex M formula. These two transformations break query folding because they force Power Query to perform operations that cannot be translated into the native query language of the source database, such as SQL. Pivoting restructures data from rows to columns, requiring grouping and aggregation that most databases cannot fold back into a single SELECT statement, while complex custom M formulas introduce logic that the source engine cannot interpret, causing Power Query to pull all data locally before applying the transformation. On the PL-300 exam, this tests your understanding of query folding as a performance optimization concept—a common trap is assuming all transformations fold equally, but any step that introduces non-native logic or structural reshaping will stop folding. Remember the memory tip: if it reshapes or calculates outside the source’s language, folding stops.
This PL-300 practice question tests your understanding of prepare the data. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 transformations in Power Query are most likely to cause Query Folding to stop? (Select two.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Pivot columns.
Pivoting typically cannot be folded.
Filter rows based on a date column.
Why wrong: Filtering usually folds.
Remove columns.
Why wrong: Removing columns folds.
Rename a column.
Why wrong: Renaming is foldable.
Add a custom column with a complex M formula.
Custom columns often break folding.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Pivot columns.
Option A is correct because Pivot columns in Power Query often require a transformation that cannot be translated into a native SQL query, causing Query Folding to break. When you pivot a column, the engine must restructure data from rows to columns, which typically involves operations like grouping and aggregation that many source systems (e.g., SQL Server) cannot fold back to a single SELECT statement. This forces Power Query to pull all data locally before applying the pivot, stopping folding.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Pivot columns.
Why this is correct
Pivoting typically cannot be folded.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Filter rows based on a date column.
Why it's wrong here
Filtering usually folds.
Remove columns.
Why it's wrong here
Removing columns folds.
Rename a column.
Why it's wrong here
Renaming is foldable.
Add a custom column with a complex M formula.
Why this is correct
Custom columns often break folding.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often assume any transformation that changes data structure (like pivot) or uses custom logic will break folding, but they may overlook that simple operations like filtering, removing columns, or renaming are fully foldable, while only complex or non-native operations cause folding to stop.
Detailed technical explanation
Query Folding relies on the Power Query engine's ability to translate M expressions into native queries (e.g., T-SQL for SQL Server). When a transformation like Pivot columns or a custom column with non-trivial M code is applied, the engine cannot generate a corresponding SQL statement, so it downloads the entire dataset to the mashup engine for processing. In real-world scenarios, this can cause significant performance degradation with large datasets, as the data must be transferred over the network and processed in memory, bypassing source-side optimizations like indexes or parallel execution.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Prepare the data — This question tests Prepare the data — Read the scenario before looking for a memorised answer..
The correct answer is: Pivot columns. — Option A is correct because Pivot columns in Power Query often require a transformation that cannot be translated into a native SQL query, causing Query Folding to break. When you pivot a column, the engine must restructure data from rows to columns, which typically involves operations like grouping and aggregation that many source systems (e.g., SQL Server) cannot fold back to a single SELECT statement. This forces Power Query to pull all data locally before applying the pivot, stopping folding.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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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