PL-300 Prepare the data Practice Question
You are preparing data for a Power BI report. You have a query that connects to a REST API that returns JSON data. The JSON response contains a nested array of order details under an 'Orders' field. You need to expand the nested array so that each order becomes a row in the table. What should you do in Power Query?
⚠ Common exam trap
Many candidates confuse the Expand operation with Unpivot, as both can create additional rows but serve different purposes.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the 'Expand' button on the 'Orders' column and select all fields.
Expanding the nested array column is the correct method to flatten JSON data in Power Query. The 'Expand' button appears when a column contains structured values such as lists or records. Expanding a list column creates a new row for each element, which is exactly what is needed to turn each order into a row. Other transformations like unpivot, split, or group by do not handle nested structures and would produce incorrect results.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use the 'Group By' transformation on the 'Orders' column.
Why it's wrong here
Group By aggregates rows based on common values, which is the opposite of expanding nested data. Applying Group By to the 'Orders' column would combine rows rather than create new rows for each order. It would not flatten the nested array and would likely lose detail. This is not the correct transformation for expanding nested JSON structures.
- ✗
Use the 'Split Column' transformation by a delimiter.
Why it's wrong here
Split Column is used to divide a text column into multiple columns based on a delimiter or number of characters. It does not work on structured data like arrays or records. The 'Orders' column contains a nested table or list, not a text string with delimiters, so splitting would not produce the desired rows. This approach would fail to extract the order details.
- ✓
Use the 'Expand' button on the 'Orders' column and select all fields.
Why this is correct
The 'Expand' button on a column containing structured values (like a nested array) allows you to expand the array elements into new rows, effectively flattening the nested data. This is the correct way to turn each order into a row. Selecting all fields ensures all order details are included. This transformation is standard when working with JSON or XML data in Power Query.
- ✗
Use the 'Unpivot Columns' transformation on the 'Orders' column.
Why it's wrong here
Unpivot Columns is used to transform wide tables into tall tables by rotating columns into rows, not to expand nested arrays. Applying unpivot to a column containing arrays would not correctly flatten the nested structure; it would treat the array as a single value and likely produce errors or incorrect results. This is not the right transformation for nested JSON.
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Last reviewed September 2026 · checked against the official Microsoft exam blueprint
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