Welcome, data enthusiasts and aspiring Power BI professionals! If you’re gearing up for a Power BI interview, you’re probably aware of the dynamic nature of the business intelligence world. To help you ace your interview, we’ve compiled a comprehensive guide to Power BI interview questions covering the spectrum from basics to advanced concepts.

Power BI is a powerful business analytics tool developed by Microsoft. It provides interactive visualizations and business intelligence capabilities with an interface that is easy to use for creating reports and dashboards. As the demand for Power BI professionals is rising, it’s crucial to be well-prepared for Power BI interviews. Read on to crack the Power BI interview questions.

1. What is the main difference between Direct Query mode and Import mode in Power BI?
   Expected Answer:
   Import Mode: The data is pulled into Power BI, where queries are executed against an in-memory dataset. Therefore, it offers better performance.
   Direct Query Mode: Data resides in the source system; queries are executed in real-time. Suitable for big data or for data that changes very rapidly but may be slower
   2. What are some of the main differences between a Power BI dashboard and report?
   Expected Answer:
   Dashboard:
   Single-page, interactive visualizations.
   Cannot apply slicer-based filtering natively.
   Developed in Power BI Service.
   Report:
   Multi-page, interactive visuals.
   Supports slicers and drill-throughs.
   Developed in Power BI Desktop.
   3. How does Power BI refresh data, and what are the data refresh types?
   Expected Answer:
   Power BI supports the following types of data refresh:
   On-demand refresh: Manually initiated by the user.
   Scheduled refresh: Scheduled on a predefined schedule in the Power BI Service.
   Automatic refresh (DirectQuery): Refresh happens automatically for DirectQuery or live connection datasets.
   Live/Real-time streaming: For real-time data feeds using APIs or streaming datasets.
   4. What is a hierarchy in Power BI, and how is it created?
   Expected Answer:
   A hierarchy is a logical structure used to organize data into levels, such as Year > Quarter > Month > Day.
   Create a hierarchy in Power BI by dragging fields into one another in the Fields pane.
   5. What are Power BI bookmarks, and how do they work?
   Expected Answer:
   Bookmarks snap a copy of a report page to include filters, slicers, and visuals
   Used for:
   To make navigation buttons
   Highlighting certain data points in reports for storytelling
   Report interactivity simplification
   6. How do you work with the "What-If" parameter in Power BI?
   Expected Answer:
   The "What-If" parameter enables users to view scenarios by changing values in real-time.
   In the "Modeling" tab create a parameter
   Apply it within DAX calculations where change is based on a user's input
   7. What is the role of the CALCULATE function in DAX? Give an example.
   Correct Response:
   The CALCULATE function adjusts the context of calculation
   Example:
   DAX
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   Sales Amount for 2023 = CALCULATE(SUM(Sales[SalesAmount]), YEAR(Sales[OrderDate]) = 2023)
   8. What is drill-through in Power BI? How is it different from drill-down?
   Expected Answer:
   Drill-through: It allows navigation from a summary page to a detailed report page by choosing specific data points.
   Drill-down: It allows the exploration of hierarchical data within the same visual, for example, Year > Month > Day.
   9. How do you leverage Power BI to create custom tooltips?
   Expected Answer:
   Custom tooltips are additional contextual information that can be displayed on hover over visuals.
   Create a new report page, add "Tooltip" to the Page Information, and specify the tooltip layout.
   Associate the custom tooltip with a visual on the Visualizations pane.
   10. How do you implement dynamic titles in Power BI?
   Expected Answer:
   Dynamic titles change as user interaction (filters, slicers).
   Steps
   Create a DAX measure, for example
   DAX
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   Title = "Sales Report for " & SELECTEDVALUE(Sales[Region], "All Regions")
   Apply the measure to the Title property of the visual.
   Let me know if you'd like detailed explanations or examples for any of these!

 

 

11. How can you optimize DAX expressions in Power BI for performance?
Explanation
DAX optimization makes reports more responsive and reduces memory usage.
Use Aggregations: Use column-based calculations like SUM instead of row-based calculations like SUMX.
Avoid Complex Calculations in Visuals: Use pre-calculated measures instead of doing on-the-fly calculations in visuals.
Reduce FILTER Usage: Replace dynamic filters with simpler conditions or pre-calculated columns.
Use Variables: Avoid redundant calculations by storing intermediate results in variables.
DAX
Copy
Optimized Measure =
VAR Temp = SUM(Sales[SalesAmount])
RETURN Temp * 0.1
12. What is the difference between STAR schema and SNOWFLAKE schema in Power BI? Which is preferred?
Detailed Explanation:


STAR Schema:
Normalized central fact table with denormalized dimension tables.
Simplifies design and facilitates faster query performance.
For example, a sales table linked to customer, product, and date tables.
SNOWFLAKE Schema:
Dimension tables are normalized or broken into multiple related tables.
More storage-efficient but increases query complexity.
Preference: STAR schema is better for Power BI because:

It reduces the number of joins.
Improves data model readability.
Enhances DAX performance.
13. Explain the concept of Composite Models in Power BI.
Detailed Explanation:
Composite Models allow combining data from different sources or modes (DirectQuery and Import).
How it Works:
Part of the data is imported for faster performance.
Frequently changing or large datasets use DirectQuery for real-time access.
Example Use Case:
Import historical sales data.
Use DirectQuery for live sales data and illustrate real-time insights.
Constraint: Overusing relationships between Import and DirectQuery tables may lead to performance issues.
14. What are Aggregations in Power BI, and what are their benefits toward improving performance?
Detailed Explanation:
Aggregations refer to pre-calculated summaries of data that are stored within the model to avoid constantly querying the detailed data.
Use Case: Aggregate the sales data by region and year in datasets with billions of rows.
Implementation:
Identify commonly used metrics (e.g., Total Sales).
Create an aggregated table using summarization (SUM, COUNT, etc.).
Use "Manage Aggregations" in Power BI Desktop to map details to the aggregated table.
15. How do you implement Incremental Data Refresh in Power BI?
Detailed Explanation:
Incremental refresh ensures that only new or changed data is updated during a data refresh.
Steps to Implement:
Create two parameters in Power Query: RangeStart and RangeEnd.
Filter the data source on these basis to load the data according to the defined range.
configure incremental refresh policy in the Power BI Desktop under model settings;
Publish the report to power BI service;
16 What is the function of tabular editor power BI?
Explanation 
Tabular Editor is used for an outside edit of power BI Models. 
advantages. 
Edit mass measures; calculated columns and hierarchies 
Generate complex scripts DAX; 
Modify model structure in the process.
Example: Replace all column names in a data set with code changes instead of editing individually.
17. How do you create Role-Level Security (RLS) using DAX?
Explanation in Detail
Role-Level Security limits which rows a user can see, according to their role
Implementation
Create roles within Power BI Desktop by selecting Modeling > Manage Roles.
DAX filters. For example
DAX
Copy code
[Region] = USERNAME()
Deploy the report to Power BI Service
Assign users or groups to the roles
Dynamic RLS Example:
Use a lookup table to map the users to regions and apply dynamic filtering on the data.
18. What are Power BI Dataflows, and when to use them?
Detailed Explanation:
Dataflows are cloud-level ETL tools available in Power BI to prepare and transform the data
When to use
You have large-scale ETL activities that need to be reused across several reports
Using the same data model on different reports
Key features
Data integration with the Azure Data Lake for Storage.
Transformation should happen using Power Query.
19. What is the difference between Paginated Reporting in Power BI and a standard Power BI reports?
Explanation:
Paginated Reports
Reports for Print or Export
Ideal candidate for operational reports like bills and inventory reports.
Create using Power BI Report Builder.
Difference
Standard Power BI Reports
Interactive reports: Visualization
Paginated reports
Printable and are meant to be exported: PDF/Excel
20. How do you work with performance issues on massive datasets in Power BI?
Detailed Explanation:
Performance Tuning guarantees quick and reactive reports.
Methods
Optimize Data Model
Eliminate unused rows/columns.
Apply Star Schema
Apply Aggregation: Pre-compute measurements to lighten query load
Reduce Visual Complexity: Simplify visuals and data point on charts
Optimize Queries: Index the source database and minimize joins
Keep Track of Performance: Identify bottlenecks using the Performance Analyzer in Power BI Desktop.