Prepare & Transform Data (Power Query)
37 free practice questions with explanations
PassNova has 37 free Microsoft PL-300 (Power BI) practice questions on Prepare & Transform Data (Power Query), each with a clear explanation. Practise them in the browser with instant feedback — 100% free, no sign-up, on any device. Updated for 2026.
Prepare & Transform Data (Power Query): example questions & answers
Here are 6 example questions from this topic. Practise the full set of 37 free in the browser.
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In Power Query, what does 'query folding' refer to?
- A Caching query results locally to speed up model refresh
- B Merging two queries into one combined table
- C Translating transformation steps back into a native query (e.g. SQL) executed by the source ✓
- D Collapsing applied steps into a single group for readability
Answer: Query folding pushes transformation steps back to the source as a native query (such as SQL), so the source does the work and less data is transferred to Power BI.
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Which Power Query transformation is most likely to BREAK query folding against a SQL Server source?
- A Removing a column
- B Adding a custom column that uses a function with no SQL equivalent ✓
- C Renaming a column
- D Filtering rows on a column value
Answer: Adding a custom column that relies on an M function with no SQL translation forces evaluation in the mashup engine, breaking folding from that step onward. Simple filters, renames and column removals usually fold.
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In the Power Query Editor, which data-profiling feature shows the percentage of valid, error, and empty values in each column?
- A Column distribution
- B Column profile
- C Column statistics
- D Column quality ✓
Answer: Column quality displays the proportion of valid, error and empty values for each column, helping you spot data issues before loading.
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You want to combine two queries by stacking their rows on top of each other (a UNION-style operation). Which Power Query operation do you use?
- A Append Queries ✓
- B Merge Queries
- C Group By
- D Pivot Column
Answer: Append Queries stacks rows from multiple queries with matching structure (like SQL UNION). Merge Queries joins tables side-by-side on a key column (like a JOIN).
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By default, where does the data-profiling preview in Power Query calculate its statistics from?
- A Only rows that contain errors
- B The entire dataset regardless of size
- C The top 1,000 rows of the preview ✓
- D A random 10% sample of the data
Answer: By default, profiling is based on the top 1,000 rows. You can switch to 'Column profiling based on entire data set' at the bottom of the window for a full scan.
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Which M function keeps only the rows of the step 'Source' where [Country] equals "UK"?
- A Table.SelectRows(Source, each [Country] = "UK") ✓
- B Table.Keep(Source, "Country", "UK")
- C Table.SelectColumns(Source, each [Country] = "UK")
- D Table.FilterColumns(Source, [Country] = "UK")
Answer: Table.SelectRows filters rows using a predicate function; the each keyword creates the row-level condition. Table.SelectColumns chooses columns, not rows.