Real Time Power BI Interview Questions and Answers

Power BI Interview Q&A · All 10 parts, 70 questions

This page lists every post in the Real Time Power BI Interview Questions and Answers series. There are 10 parts and 70 questions, the ones hiring managers really ask: licensing, storage modes, Power Query, data modeling, DAX, time intelligence, performance, security, deployment and real project scenarios.

Each part has a video and a written post with the short answer to say first, the DAX or M code, and results on a small sample data set you can rebuild yourself. Click a part to read it, or click a question to jump straight to its answer.

Part 1: Architecture, Components and Licensing

1. What are the main components of Power BI, and how do they fit together?
2. What do you do in Power BI Desktop, and what do you do in the Power BI service?
3. What is a semantic model, and how is it different from a report?
4. What are workspaces and apps, and how should you share content with a large audience?
5. What is the difference between Power BI Pro, Premium Per User and a Fabric capacity?
6. What is an on-premises data gateway, and when do you need one?
7. Scenario: 20 report creators and 2,000 viewers. What licensing do you recommend?

Part 2: Import, DirectQuery and Direct Lake

1. What are the storage modes in Power BI: Import, DirectQuery, Direct Lake, plus Dual and live connection?
2. Import vs DirectQuery: when would you choose each?
3. What is Direct Lake, how is it different from Import and DirectQuery, and what is fallback?
4. What is a composite model, and what is Dual storage mode?
5. What are aggregations (user-defined aggregation tables), and when do they help?
6. What is the difference between a live connection and DirectQuery to a Power BI semantic model or Analysis Services?
7. Scenario: the business wants near real-time sales on a 2-billion-row table, but DirectQuery reports are slow. What design do you propose?

Part 3: Power Query and Query Folding

1. What is Power Query, what is the M language, and where does Power Query run?
2. What is query folding, and how do you check whether a step folds?
3. Which steps break query folding, and how should you order your steps?
4. What is the difference between Reference and Duplicate, and between Merge and Append?
5. How do parameters and incremental refresh work, and why must the filter fold?
6. What are privacy levels, and how do you fix a Formula.Firewall error?
7. Scenario: refreshing a 50-million-row SQL Server table takes two hours and sometimes times out. What do you do?

Part 4: Data Modeling and Relationships

1. Why do we build a star schema instead of one big flat table?
2. What is the difference between a fact table and a dimension table, and what is the grain?
3. What relationship cardinalities are there, what is cross-filter direction, and why should you avoid bidirectional filters?
4. What is an inactive relationship, what does USERELATIONSHIP do, and how do you handle Order Date and Ship Date?
5. How do you model a many-to-many relationship: bridge table or many-to-many cardinality? What is a limited relationship?
6. Why do you need a dedicated date table, what does Mark as date table do, and why turn off Auto date/time?
7. Scenario: the budget is by category and month, but sales are by product and day. How do you model it?

Part 5: DAX Fundamentals and Filter Context

1. What is the difference between a measure and a calculated column, and when do you use each?
2. What is the difference between row context and filter context?
3. What does CALCULATE do, and what is context transition?
4. What is the difference between SUM and SUMX?
5. How do you calculate percent of total, and what do ALL and REMOVEFILTERS do?
6. Why should you use variables and DIVIDE in your measures?
7. Scenario: the total row in a table does not equal the sum of the rows. Why, and how do you fix it?

Part 6: Time Intelligence and Advanced DAX

1. What do you need for time intelligence to work in Power BI?
2. How do you calculate year-to-date sales in DAX?
3. How do you compare with last year, and calculate year-over-year growth and percent?
4. What is calendar-based time intelligence, and why does it matter for fiscal, 4-4-5 or week-based calendars?
5. What are visual calculations, and when would you use them instead of a model measure?
6. What are calculation groups and DAX user-defined functions, and how do they reduce duplicated measures?
7. Scenario: Finance's fiscal year starts in July, and they want YTD, prior-year YTD and a rolling 12 months that all match their numbers. How do you build it?

Part 7: Performance Optimization

1. How do you find out why a report page is slow?
2. How does the VertiPaq engine compress data, and what makes an import model big?
3. How do you reduce the size of a semantic model?
4. How do you write faster DAX?
5. What are aggregations and composite models, and when do you use them?
6. How does report design affect performance, and what is the Best Practice Analyzer?
7. Scenario: the CEO says the sales dashboard takes 15 seconds to load. Walk me through what you do.

Part 8: Row-level Security and Governance

1. What is row-level security, and what is the difference between static and dynamic RLS?
2. How do you implement dynamic RLS with USERPRINCIPALNAME()?
3. Where are RLS roles defined and members assigned, and who bypasses RLS?
4. What is object-level security (OLS), and how is it different from RLS?
5. What are the workspace roles, and how do you share content: apps, direct sharing or Build permission?
6. How do you govern Power BI content with sensitivity labels, endorsement, tenant settings and lineage?
7. Scenario: a regional manager says she can see other regions' sales in the report. How do you investigate and fix it?

Part 9: Deployment, Git and Refresh

1. What are PBIX, PBIP, PBIR and TMDL, and why do they matter for source control?
2. How do deployment pipelines work, and what do they deploy?
3. How does Fabric Git integration work, and how is it different from deployment pipelines?
4. What are the limits of scheduled refresh, and how do you find out when a refresh fails?
5. How does incremental refresh work?
6. What is the XMLA endpoint, and how do you refresh only some tables or partitions?
7. Scenario: someone published straight to production and broke the CFO's report. How do you make sure it never happens again?

Part 10: Real-world Manager Scenarios

1. Scenario: two reports show different revenue numbers for the same month. How do you find out why?
2. Scenario: a stakeholder asks for a new KPI by tomorrow. How do you gather requirements and deliver it?
3. Scenario: users export everything to Excel. What do you do?
4. Scenario: leadership wants AI and Copilot in Power BI. What do you need to set up?
5. Scenario: the refresh failed at 6 AM and the executive meeting is at 9. Walk me through it.
6. Scenario: how do you handle a request for a report with 40 visuals on one page?
7. Scenario: how would you take over a messy Power BI environment with 300 reports?

Each part has a matching video on the TechBrothersIT YouTube channel, in the "Power BI Interview Questions and Answers" playlist.