Basic Questions
1. What is Power BI and what are its main components?
Power BI is Microsoft's business intelligence platform for building interactive reports and dashboards. Its main components are Power BI Desktop (report building), Power BI Service (publishing/sharing), and Power BI Mobile (viewing on the go).
2. What's the difference between a report and a dashboard?
A report is a multi-page file built in Desktop with detailed, interactive visuals. A dashboard is a single-page pinboard in the Power BI Service that pulls visuals from one or more reports for a high-level overview.
3. What data sources can Power BI connect to?
Excel, CSV, SQL Server and other databases, SharePoint, web APIs, Google Analytics, Salesforce, and dozens more — Power BI supports well over 100 connectors.
DAX Questions
4. What's the difference between a measure and a calculated column?
A measure is calculated dynamically based on filter context (e.g. a total that changes as you filter). A calculated column is computed once per row when data refreshes and stored in the table.
5. What does CALCULATE do?
CALCULATE changes the filter context a calculation runs in — it's how you apply conditions to a measure, like calculating sales only for a specific year or region.
6. What's the difference between SUM and SUMX?
SUM adds up values in a single column directly. SUMX is an iterator — it goes row by row, evaluates an expression for each, then sums the results. Use SUMX when the calculation itself needs to happen per row (e.g. Quantity × Price) before summing.
Data Modeling Questions
7. What is a star schema and why does it matter?
A star schema is a data model with a central fact table (transactions/events) connected to surrounding dimension tables (Product, Customer, Date). It's the recommended structure in Power BI because it's simpler, faster, and less error-prone than flat, wide tables.
8. What's the difference between one-to-many and many-to-many relationships?
One-to-many is the standard, safest relationship (e.g. one Customer to many Orders). Many-to-many relationships are allowed but require more care — they can cause ambiguous filtering and unexpected results if not modeled carefully.
Scenario Questions
9. "Your dashboard is running slowly — what would you check?"
Good answer covers: unnecessary calculated columns instead of measures, overly complex DAX with nested iterators, too many visuals on one page, importing unused columns/rows, and whether Import mode vs DirectQuery is appropriate for the data size.
10. "How would you show year-over-year growth?"
Explain using a measure with CALCULATE and a time-intelligence function like SAMEPERIODLASTYEAR, then computing the percentage difference between this period and that comparison period.
Interview Tips
Interviewers care more about how you reason through a problem than whether you recite the "correct" textbook answer. Talk through your thinking, even for questions you're unsure about.
Be ready to walk through a project you've actually built — this matters more than any list of memorized answers.