Prepare & Transform Data (Power Query)

In Power Query, what does 'query folding' refer to?

• ACaching a local copy of the query results inside the model so later refreshes read from that cache
• BMerging two queries into one combined table
• CTranslating transformation steps back into a native query (e.g. SQL) executed by the source✓
• DCollapsing several applied steps into a single named group so the step list is easier to read

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.

Which Power Query transformation is most likely to BREAK query folding against a SQL Server source?

• ARemoving an unused column from the table immediately after the navigation step
• BAdding a custom column that uses a function with no SQL equivalent✓
• CRenaming a column to a friendlier business name in the Power Query Editor
• DFiltering rows where a column value matches a single literal string

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.

In the Power Query Editor, which data-profiling feature shows the percentage of valid, error, and empty values in each column?

• AColumn distribution
• BColumn profile
• CColumn statistics
• DColumn quality✓

Answer: Column quality displays the proportion of valid, error and empty values for each column, helping you spot data issues before loading.