✅ Power BI Interview Questions with Answers

1. What is DAX? 
DAX (Data Analysis Expressions) is a formula language in Power BI used to create calculated columns, measures, and tables (e.g., SUM(), CALCULATE(), FILTER()) for business logic and KPIs.

2. What is the difference between Power Query and Power Pivot? 
• Power Query: used for data loading, cleaning, and transforming (ETL) before loading into the model.
• Power Pivot: in‑memory data model and engine for DAX calculations and relationships (used during/after load).

3. What is the difference between measure vs calculated column? 
• Measure: calculated at query time, used in visuals (e.g., summaries, ratios).
• Calculated column: computed at refresh time, stored in the model (uses more memory). Prefer measures for aggregations.

4. Explain CALCULATE() function. 
CALCULATE() changes the context of a calculation by applying filters. 
Example: Total Sales = CALCULATE(SUM(Sales[Amount]), Sales[Region] = "West") computes sum only for West region.

5. What are relationships (1:M, M:M)? 
• 1:M (one‑to‑many): one row in the “1” table links to many rows in the “M” table (most common).
• M:M (many‑to‑many): handled via an intermediate bridge table with foreign keys on both sides.

6. How do you handle many‑to‑many? 
Create a bridge table (junction table) that contains foreign keys to both related tables. Then set 1:M relationships from each original table to the bridge.

7. What is row‑level security (RLS)? 
RLS restricts which rows a user can see in a report (e.g., by SalesRegion = “UserRegion”). Defined in the model with DAX filter expressions and applied by user roles.

8. How do you setup incremental refresh? 
• Mark your tables as “incrementally refreshable” in the model.
• Define a date/time column and ranges (e.g., last 3 years full, last 60 days incremental).
• Set refresh schedule in the Power BI service with gateways if needed.

9. What is the difference between filters vs slicers? 
• Filters: rules applied behind the scenes (e.g., in page/report level filters) that always apply.
• Slicers: interactive controls on the report canvas that users click to change what data is shown.

10. What is a data model? 
A data model is the structure in Power BI that holds tables, relationships, calculated columns, measures, and hierarchies, forming the semantic layer for reporting.

11. How do you publish and share reports? 
• Publish from Power BI Desktop to a workspace in Power BI Service.
• Share via apps, workspaces, or by granting access to specific users/groups; use RLS and sharing permissions to control who sees what.

12. What is Performance Analyzer tool? 
Performance Analyzer in Power BI Desktop records how long each visual takes to render and which DAX queries run, helping identify slow visuals or large queries.

13. How do you create month‑on‑month growth DAX? 
MoM Growth =
VAR CurrentSales = [Total Sales] 
VAR PreviousSales = CALCULATE([Total Sales], DATEADD('Date'[Date], -1, MONTH)) 
RETURN 
DIVIDE(CurrentSales - PreviousSales, PreviousSales)

14. How do you use custom visuals? 
Download a custom visual from the marketplace, add it to the report in Power BI Desktop or Service, then configure like a native visual (fields, formatting, interactivity).

15. What is gateway for refresh? 
An on‑premises gateway connects Power BI Service to data sources behind your firewall (e.g., SQL Server, file shares). It enables scheduled refresh for datasets that pull from those sources.

16. What is a .pbix file? 
A .pbix file is the Power BI Desktop project file that contains the report layout, queries, data model, and DAX logic. It can be opened in Power BI Desktop or published to the service.

17. What are quick measures examples? 
Quick measures are auto‑generated DAX calculations with a UI. Examples: 
• Average of a column.