Power BI interview questions

Basic Power BI interview questions for freshers

1. 01

   What is Power BI?

   Basic

   Power BI is Microsoft's business intelligence tool. It connects to data sources such as Excel, SQL databases and cloud apps, cleans and models the data, and turns it into interactive reports and dashboards that can be shared across a company.

2. 02

   What are the main parts of Power BI?

   Basic

   • Power BI Desktop: the free Windows app where you connect data, model it and build reports.
   • Power BI Service: the cloud service where reports are published, shared, refreshed and turned into dashboards.
   • Power BI Mobile: apps for viewing reports on a phone.
   • On-premises data gateway: lets the Service refresh data that sits on a company's own servers.
3. 03

   What is the difference between a report and a dashboard?

   Basic

   A report can have many pages of interactive visuals built from one semantic model (dataset), and is created in Desktop or the Service. A dashboard is a single page in the Power BI Service made of tiles pinned from one or more reports, used for a quick overview.

4. 04

   What are the building blocks of Power BI?

   Basic

   Visualisations (charts, tables, cards), datasets or semantic models (the data and its model), reports (pages of visuals), dashboards (pinned tiles) and tiles (single visuals on a dashboard).

5. 05

   What data sources can Power BI connect to?

   Basic

   Files (Excel, CSV, PDF, folders), databases (SQL Server, Oracle, MySQL, PostgreSQL), cloud services (SharePoint, Azure, Salesforce, Google Analytics) and web pages or APIs, among many others.

6. 06

   What are slicers?

   Basic

   Slicers are on-page filters that users click, such as a list of regions or a date range. They filter the other visuals on the page and can be synced across pages.

Power Query and data preparation questions

7. 07

   What is Power Query?

   Basic

   Power Query is the data preparation tool inside Power BI (and Excel). You use it to connect to sources and clean data: remove columns, change data types, split columns, filter rows, unpivot and combine tables. Each step is recorded and re-applied on every refresh. Its formula language is called M.

8. 08

   What is the difference between Merge and Append queries?

   Basic

   Merge joins two tables side by side on a matching column, like a SQL join or VLOOKUP, adding columns. Append stacks tables with the same columns one below the other, adding rows, such as January and February sales files.

9. 09

   How do you handle missing or wrong values in Power Query?

   Intermediate

   Filter out blank rows, use Replace Values for known errors, Fill Down for values that should repeat, Remove Errors or Replace Errors for conversion problems, and set the correct data type for each column early.

10. 10

    What is unpivoting, and when do you need it?

    Intermediate

    Unpivoting turns columns into rows. A sheet with one column per month (Jan, Feb, Mar) becomes two columns, Month and Value. Power BI models and charts work best with this long, narrow shape.

Data modelling questions

11. 11

    What is a star schema?

    Basic

    A model with one central fact table holding the numbers (sales, quantities) and dimension tables around it holding the descriptions (date, product, customer, region), each linked to the fact table by a one-to-many relationship. It is the recommended shape for Power BI models.

12. 12

    What types of relationships does Power BI support?

    Intermediate

    One-to-many (the most common, from a dimension to a fact table), one-to-one and many-to-many. Each relationship also has a cross-filter direction: single (the usual choice) or both.

13. 13

    What is the difference between an active and an inactive relationship?

    Advanced

    Only one relationship between two tables can be active, and it is the one filters use by default. Others are inactive (shown as dotted lines). Use USERELATIONSHIP inside CALCULATE to use an inactive one in a measure, for example ship date instead of order date.

14. 14

    What is the difference between Import, DirectQuery and Live connection?

    Intermediate

    Import copies the data into the Power BI file: fastest, but only as fresh as the last refresh. DirectQuery leaves the data in the source and queries it each time a visual loads: always current, but slower and with some DAX limits. Live connection connects to an existing published model or Analysis Services model. A composite model mixes Import and DirectQuery.

15. 15

    Why do you need a separate date table?

    Intermediate

    Time-intelligence functions such as TOTALYTD and SAMEPERIODLASTYEAR need a table with one row for every date and no gaps. Create one (for example with CALENDAR or CALENDARAUTO), relate it to your fact table and mark it as a date table.

DAX interview questions

16. 16

    What is DAX?

    Basic

    Data Analysis Expressions, the formula language of Power BI. You use it to create measures, calculated columns and calculated tables.

17. 17

    What is the difference between a calculated column and a measure?

    Basic

    A calculated column is computed row by row when the data refreshes and stored in the model, like a new column in Excel. A measure is computed when a visual asks for it, using the current filters, and is not stored. Use measures for totals, ratios and anything that should change with slicers.

    Profit = Sales[Amount] - Sales[Cost]            -- calculated column
    Total Sales = SUM(Sales[Amount])                 -- measure

18. 18

    What is the difference between row context and filter context?

    Intermediate

    Row context means "the current row", and exists in calculated columns and iterator functions such as SUMX. Filter context is the set of filters coming from slicers, visuals and CALCULATE, and decides which rows a measure sees.

19. 19

    What does CALCULATE do?

    Intermediate

    CALCULATE evaluates an expression in a changed filter context. It is the most important DAX function: you use it to add, remove or replace filters, such as sales for one region only.

    North Sales = CALCULATE(SUM(Sales[Amount]), Sales[Region] = "North")

20. 20

    What is the difference between SUM and SUMX?

    Intermediate

    SUM adds up one column. SUMX goes through a table row by row, evaluates an expression for each row and adds the results, so it can sum something that is not stored, such as quantity times price.

    Revenue = SUMX(Sales, Sales[Qty] * Sales[Price])

21. 21

    What do ALL and ALLEXCEPT do?

    Intermediate

    ALL removes filters from a table or column, which is how you get a grand total to compute a percentage of total. ALLEXCEPT removes all filters from a table except the columns you name.

    % of Total = DIVIDE(SUM(Sales[Amount]), CALCULATE(SUM(Sales[Amount]), ALL(Sales)))

22. 22

    Why use DIVIDE instead of the / operator?

    Basic

    DIVIDE handles division by zero safely: it returns blank, or an alternate value you choose, instead of an error.

23. 23

    How do you calculate year-to-date and last year's sales?

    Intermediate

    With time-intelligence functions over a marked date table.

    Sales YTD = TOTALYTD(SUM(Sales[Amount]), 'Date'[Date])
    Sales LY  = CALCULATE(SUM(Sales[Amount]), SAMEPERIODLASTYEAR('Date'[Date]))

24. 24

    What is the difference between RELATED and RELATEDTABLE?

    Advanced

    RELATED brings a single value from the "one" side of a relationship into a row on the "many" side, such as a product's category into the sales table. RELATEDTABLE goes the other way and returns all the related rows from the "many" side.

Reports, sharing and security questions

25. 25

    What is the difference between drill-down and drill-through?

    Intermediate

    Drill-down moves to a lower level of a hierarchy inside the same visual, such as year to quarter to month. Drill-through jumps to another report page filtered to the item you right-clicked, such as a detail page for one customer.

26. 26

    What are bookmarks used for?

    Intermediate

    Bookmarks save the current state of a report page: filters, slicers and which visuals are visible. They are used for buttons that switch views, guided storytelling and toggling between a chart and a table.

27. 27

    What is row-level security (RLS)?

    Intermediate

    RLS limits the rows each user can see. You create roles with DAX filters in Desktop, such as Region equals "South", publish, then assign users or groups to each role in the Power BI Service.

28. 28

    How does scheduled refresh work?

    Intermediate

    After you publish an Import model to the Service, you set a refresh schedule in its settings. Data on a company's own servers needs an on-premises data gateway. How often you can refresh depends on the licence or capacity.

29. 29

    What are workspaces and apps?

    Basic

    A workspace is a shared area in the Power BI Service where a team builds and stores reports, models and dashboards. An app packages selected content from a workspace and publishes it to a wider audience, who can view it but not edit it.

30. 30

    How would you make a slow report faster?

    Advanced

    Remove unused columns and rows, use a star schema, prefer measures to calculated columns, reduce the number of visuals per page, avoid high-cardinality columns such as full timestamps, and use Performance Analyzer to find the slow visuals.

How to prepare for a Power BI interview

1. 01

   Build one complete dashboard from a public dataset: import it, clean it in Power Query, model it as a star schema with a date table, write five or six measures and publish it.

2. 02

   Learn the ten DAX functions asked most: SUM, SUMX, COUNTROWS, DISTINCTCOUNT, CALCULATE, FILTER, ALL, DIVIDE, RELATED and one time-intelligence function such as TOTALYTD.

3. 03

   Practise explaining the difference between a calculated column and a measure, and between row and filter context, with an example from your own project.

4. 04

   Revise SQL joins and GROUP BY and Excel pivots and lookups, because Power BI roles usually test them too. Our Excel interview questions cover the Excel side.

5. 05

   Prepare to walk through your dashboard in two minutes: the business question, the data, the model, the key measures and what a manager learns from it.

Which roles ask Power BI interview questions?