Power Query Interview Questions and Answers 2026

Power Query is one of the most used tools inside Power BI. It is used to connect, clean, and shape data before it goes into a report. Because of this, most Power BI interviews include a good number of Power Query questions.

This article has 50 common Power Query interview questions and answers. We cover the basics, the editor, data transformations, the M language, and advanced topics. Code examples are added so you can see how real M code looks. The language is kept simple and easy to follow, even if you are just starting out.

What Is Power Query?

Power Query is a data connection and transformation tool built into Power BI, Excel, and other Microsoft products. It lets you connect to many types of data, clean messy data, and shape it into the format you need before loading it into your report.

Every action you take in Power Query, like removing a column or filtering rows, is recorded as a step. This makes it easy to go back, edit, or remove any step without starting over.

Common Data Sources for Power Query

Power Query can connect to many types of data. Here are some of the most common ones asked about in interviews.

Data Source	Example
File	Excel, CSV, Text, JSON, PDF
Database	SQL Server, MySQL, Oracle
Online Service	SharePoint, Salesforce, Google Analytics
Cloud Platform	Azure SQL, Azure Data Lake
Web	Web pages and online tables
Folder	A folder full of similar files

Types of Transformations in Power Query

Interviewers often ask you to name different kinds of transformations. Here is a simple table you can use to explain them.

Transformation Type	What It Does	Example
Filter Rows	Keeps only rows that match a condition	Keep sales above 1000
Remove Columns	Deletes columns you do not need	Remove a comments column
Merge Queries	Joins two tables side by side	Add customer name to sales table
Append Queries	Stacks two tables on top of each other	Combine sales from two years
Group By	Groups rows and summarizes values	Total sales by region
Pivot / Unpivot	Changes rows into columns or columns into rows	Turn month columns into rows

Basic Power Query Interview Questions and Answers

These questions check if you understand what Power Query is and why it is used.

1. What is Power Query?

Power Query is a tool used to connect to data, clean it, and shape it before loading it into Power BI or Excel. It handles the data preparation stage of a report.

2. Where can you find Power Query in Power BI?

You can open Power Query by clicking on Transform Data in Power BI Desktop. This opens the Power Query Editor window.

3. Why is Power Query important in Power BI?

Power Query is important because raw data is often messy, with missing values, wrong formats, or extra columns. Power Query cleans this data before it reaches your report, which makes your reports more accurate.

4. What is the difference between Power Query and DAX?

Power Query is used to clean and shape data before it enters the data model. DAX is used to build calculations, like measures, after the data is already loaded.

5. Can Power Query connect to multiple data sources at once?

Yes. Power Query can connect to many data sources in the same file. You can then combine or keep them separate, depending on what your report needs.

6. What is a query in Power Query?

A query is a set of steps that connects to a data source and transforms it into the shape you want. Each table you load usually has its own query.

7. What happens when you click Close and Apply?

When you click Close and Apply, Power Query runs all the steps in your queries and loads the final, cleaned data into the Power BI data model.

8. Is Power Query only available in Power BI?

No. Power Query is also available in Excel, and in tools like Power Automate and Analysis Services. It works in a similar way across all of them.

9. What is the difference between a data source and a query?

A data source is where the raw data comes from, like a file or database. A query is the set of steps you apply to that data inside Power Query.

10. Can you undo a step in Power Query?

Yes. Since every action is saved as a step, you can click on any earlier step, edit it, or delete it. This makes it easy to fix a mistake without starting over.

Power Query Editor Interview Questions and Answers

These questions are about the Power Query Editor window and how to work inside it.

11. What is the Power Query Editor?

The Power Query Editor is a separate window where you connect to data and apply transformation steps. It shows a preview of your data as you work.

12. What is the Applied Steps pane?

The Applied Steps pane is a list on the right side of the editor that shows every transformation step you have done, in order. You can click any step to see the data at that point.

13. What is the Queries pane used for?

The Queries pane, usually on the left side, lists all the queries in your file. You can click a query to open it and see its steps.

14. How do you rename a query?

You can right-click on the query name in the Queries pane and choose Rename, or double-click the name and type a new one.

15. What is a step in Power Query?

A step is a single transformation action, like removing a column or filtering rows. Steps run in order, from top to bottom, to build the final table.

16. Can you rename a step?

Yes. You can right-click a step in the Applied Steps pane and choose Rename. This is helpful for making your steps clearer to understand later.

17. What is the formula bar in Power Query?

The formula bar shows the M code for the step you have selected. You can view or edit this code directly if you want more control.

18. How do you see the M code behind a whole query?

You can click on Advanced Editor from the View or Home tab. This opens a window showing the full M code for all the steps in that query.

19. What is a disabled load in Power Query?

A disabled load means a query is kept in the file but not loaded into the report. This is common for helper queries that are only used inside other queries.

20. How do you duplicate a query?

You can right-click on a query in the Queries pane and select Duplicate. This creates a full copy of the query with all its steps.

Data Transformation Interview Questions and Answers

These questions are about common ways to clean and reshape data using Power Query.

21. What is the difference between Merge and Append?

Merge joins two tables side by side using a matching column, similar to a VLOOKUP or SQL join. Append stacks two tables on top of each other, adding more rows.

22. What are the different types of joins used in Merge?

Common join types are Left Outer, Right Outer, Inner, Full Outer, Left Anti, and Right Anti. Each one decides which rows are kept from each table.

23. What is Group By used for?

Group By is used to combine rows and calculate a summary, like a total or average, for each group. For example, grouping sales by region.

24. What is the difference between Pivot and Unpivot?

Pivot turns row values into new columns. Unpivot does the opposite, turning columns into rows. Unpivot is often used to fix wide, spreadsheet style data.

25. How do you remove duplicate rows in Power Query?

You select the column or columns you want to check, then choose Remove Duplicates from the Home tab. Power Query keeps only the first matching row.

26. How do you split a column in Power Query?

You can right-click a column and choose Split Column. You can split by a delimiter, like a comma or space, or by a set number of characters.

27. What is the difference between Remove Columns and Remove Other Columns?

Remove Columns deletes only the columns you select. Remove Other Columns keeps only the columns you select and removes everything else.

28. How do you filter rows in Power Query?

You click the small arrow on a column header and choose a filter, like a specific value or a range. You can also use text filters, date filters, or number filters.

29. What is the Fill Down feature used for?

Fill Down copies a value from the row above into empty cells below it. It is often used to fix data where a value was only entered once for a group of rows.

30. How do you change a column’s data type?

You can click the data type icon at the top of a column and choose the correct type, like Whole Number, Text, or Date. This step is important, since wrong data types can cause errors later.

M Language and Code Interview Questions with Examples

M is the programming language behind Power Query. These questions test your knowledge of M code, with examples to help you see how it works.

31. What is the M language?

M is the language used behind Power Query. Every action you take in the editor, like a filter or a merge, is automatically written as M code.

32. How do you view the M code for a query?

You can open the Advanced Editor from the Home or View tab. It shows the full M code for every step in that query, from start to finish.

33. What is the basic structure of an M query?

An M query starts with the word let, followed by a list of steps, and ends with in and the name of the final step. Here is a simple example:

let

    Source = Excel.Workbook(File.Contents(“C:\Sales.xlsx”)),

    Sheet1 = Source{[Item=”Sheet1″]}[Data]

in

    Sheet1

34. How do you filter rows using M code?

You use the Table.SelectRows function along with a condition. Here is an example that keeps only rows where sales are above 1000:

Table.SelectRows(Source, each [SalesAmount] > 1000)

35. How do you remove a column using M code?

You use the Table.RemoveColumns function and list the column names you want to remove. Example:

Table.RemoveColumns(Source, {“Comments”, “InternalNotes”})

36. How do you add a new custom column using M code?

You use the Table.AddColumn function, giving it a new column name and a formula. Example:

Table.AddColumn(Source, “Total”, each [Quantity] * [UnitPrice])

37. How do you rename a column using M code?

You use the Table.RenameColumns function with the old and new names in a list. Example:

Table.RenameColumns(Source, {{“Amt”, “SalesAmount”}})

38. How do you change a column’s data type using M code?

You use the Table.TransformColumnTypes function. Example:

Table.TransformColumnTypes(Source, {{“OrderDate”, type date}})

39. Is M language case sensitive?

Yes. Unlike DAX, the M language is case sensitive. This means Source and source would be treated as two different names, so you need to be careful with spelling and capital letters.

40. What is the each keyword used for in M code?

The each keyword is a shortcut used to write a small function that runs on each row of a table. It is often used inside functions like Table.SelectRows and Table.AddColumn.

Advanced Power Query and Performance Interview Questions

These questions cover more advanced features and how to keep your queries running fast, which are common in senior level interviews.

41. What is query folding?

Query folding is when Power Query sends your transformation steps back to the original data source, like a SQL database, so the source does the work. This makes refreshes much faster.

42. How can you check if query folding is happening?

You can right-click a step in the Applied Steps pane and look for the option View Native Query. If this option is available, query folding is happening for that step.

43. What is a query parameter?

A query parameter is a value you can set once and reuse across many queries, such as a file path, a date, or an environment name. It makes it easy to update settings in one place.

44. How do you create a function in Power Query?

You can turn any query into a function by adding parameters to it, or by writing a custom function directly in the Advanced Editor using the M language.

45. What is the difference between a query and a function in Power Query?

A query returns a table of data. A function takes input values and returns a result, which could be a table, a number, or text. Functions can be reused with different inputs.

46. How do you combine files from a folder in Power Query?

You use the Folder connector to point to a folder, then use the Combine Files feature. Power Query reads the structure of one file and applies the same steps to every file in the folder.

47. What is the difference between a staging query and a loaded query?

A staging query is used only as a helper inside other queries and is not loaded into the report. A loaded query is turned on to load its data into the Power BI data model.

48. How do you handle errors in Power Query?

You can use options like Remove Errors or Replace Errors from the menu, or write custom M code using try and otherwise to catch and handle errors safely.

try [SalesAmount] / [Quantity] otherwise 0

49. Why should you reduce the number of steps in a query?

Fewer steps usually make a query easier to read and can also make it run faster, especially on large data sets. It is good practice to combine similar steps when possible.

50. What is a good practice when naming Power Query steps?

It is good practice to give steps clear names that explain what they do, instead of leaving default names like Changed Type1. This makes your queries much easier to understand later, or for someone else to review.

Common Merge Join Types in Power Query

This table is a quick reference for the join types used in the Merge feature.

Join Type	What It Returns
Left Outer	All rows from the first table, plus matching rows from the second
Right Outer	All rows from the second table, plus matching rows from the first
Inner	Only rows that match in both tables
Full Outer	All rows from both tables, matched where possible
Left Anti	Only rows from the first table that do not match the second
Right Anti	Only rows from the second table that do not match the first

Tips to Prepare for a Power Query Interview

• Practice connecting to a few different data sources, like Excel and a folder of files
• Get comfortable with Merge, Append, and Group By, since these come up often
• Try opening the Advanced Editor to read and understand basic M code
• Learn what query folding is and why it matters for performance
• Practice explaining the difference between a query and a function
• Keep your queries clean by naming steps clearly as you build them

Frequently Asked Questions

Final Thoughts

This list of 50 Power Query interview questions and answers covers the basics, the editor, transformations, the M language, and advanced topics like query folding. Go through each section and try explaining the answers in your own words.

The best way to get ready is to practice. Open Power BI Desktop, connect to a small file, and try the transformations covered in this article. Hands-on practice will make these questions much easier to answer in a real interview.

Similar Article