PL-300 Prepare the data Practice Question
You are working with a Power BI dataset that imports data from a web API. The API returns a JSON response containing a nested array of order details for each order. You need to flatten this nested array so that each order detail becomes a separate row in the table. Which Power Query transformation should you use?
⚠ Common exam trap
The trap here is thinking that Unpivot or Split Column can handle nested arrays, when only the Expand operation is designed for this purpose.
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
✓
Expand the column containing the array.
Expanding the column that contains the nested array is the correct way to flatten JSON data in Power Query. This creates one row per array element, duplicating the parent order fields as needed. Other transformations do not handle nested structures and would fail to produce the required row-level detail.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Transpose the table.
Why it's wrong here
Transpose swaps rows and columns but does not unnest arrays. It would not create separate rows for each order detail; instead, it would rearrange the existing table structure. This transformation is not suitable for flattening nested data.
- ✓
Expand the column containing the array.
Why this is correct
Expanding the column that holds the nested array (often a List or Record type) will create a new row for each element in the array, effectively flattening the data. This is the standard way to unnest arrays in Power Query. After expansion, related order information is repeated for each detail row, which may require further shaping.
- ✗
Use the Unpivot Columns transformation.
Why it's wrong here
Unpivot Columns transforms wide tables into tall tables by turning columns into rows, but it operates on column headers, not on nested arrays within a cell. It does not address the requirement of expanding an array into multiple rows. Unpivot is used for a different data shaping scenario.
- ✗
Use the Split Column transformation with a comma delimiter.
Why it's wrong here
Split Column is used for text values, not for arrays or lists. JSON arrays are not comma-separated text strings in Power Query; they are structured as List values. Splitting would not correctly parse the nested structure and would likely produce errors or incorrect results.
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Last reviewed September 2026 · checked against the official Microsoft exam blueprint
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