Top 25 Interview Questions with Answers for Power BI Data Analyst

Preparing for the PL-300T00 Power BI Data Analyst exam can be daunting, but with the right guidance and resources, you can ace it. This blog post provides the top 25 interview questions and answers to help you succeed in designing Microsoft Azure infrastructure solutions.

Top 25 Interview Questions with Answers for PL-300T00: Power BI Data Analyst

1. What is Power BI and what are its key components?

Power BI is a suite of business analytics tools developed by Microsoft that enables users to visualize data and share insights across an organization or embed them in an app or website. It helps organizations turn raw data into informative insights for better decision-making. The key components of Power BI include Power BI Desktop (for authoring reports), Power BI Service (cloud-based sharing and collaboration), Power BI Mobile (mobile apps), Power BI Gateway (for data refresh and connectivity), and Power BI Report Server (for on-premises report publishing). Together, they enable end-to-end data transformation, analysis, and reporting.

2. Explain the difference between Direct Query and Import mode in Power BI.

Import mode pulls the data into Power BI and stores it in a compressed, in-memory cache, which offers fast performance and rich modeling capabilities. DirectQuery, on the other hand, does not import data into Power BI. Instead, it queries the source database directly each time a report is run, ensuring real-time or near real-time data access. Import mode is preferred for speed and functionality, while DirectQuery is used when data freshness and source governance are priorities.

3. What are DAX functions and how are they used in Power BI?

DAX (Data Analysis Expressions) is a formula language used in Power BI, Excel, and other Microsoft products to define custom calculations and expressions on data models. DAX is critical for performing aggregations, filtering data contextually, creating calculated columns or measures, and implementing business logic. With DAX, analysts can define metrics like year-to-date sales, running totals, or percent growth, enabling deeper insights from data.

4. What are the main types of filters in Power BI?

• Visual-level filters: Apply to a specific visual on a report page.
• Page-level filters: Apply to all visuals on a single report page.
• Report-level filters: Apply to all pages within a report.
• Drillthrough filters: Allow users to navigate to a detailed report based on a selected data point.
• Slicer filters: Visual tools users can interact with to filter report data dynamically.

5. List some best practices for Power BI data modeling.

• Use star schema for efficient and intuitive models.
• Ensure column data types are correctly set to optimize performance.
• Avoid bidirectional relationships unless absolutely necessary.
• Create calculated measures instead of calculated columns for efficiency.
• Use surrogate keys for relationships between tables when needed.

6. What are some common data sources that Power BI can connect to?

• SQL Server and other relational databases
• Excel files and CSVs
• SharePoint and OneDrive
• Web APIs and RESTful services
• Azure services (Azure SQL DB, Azure Blob Storage, etc.)
• Online services like Salesforce, Google Analytics, and Dynamics 365

7. How does Row-Level Security (RLS) work in Power BI?

RLS in Power BI enables the restriction of data access for specific users by applying DAX filters on roles. You define roles and rules in Power BI Desktop, which are then published to the Power BI service. When a user views the report, only the data that meets the rule criteria is visible to them. This ensures data confidentiality and compliance, especially in multi-user environments.

8. Describe how you can schedule data refresh in Power BI Service.

You can configure scheduled refresh in the Power BI Service under the dataset settings. After publishing a report to the Power BI workspace, navigate to the dataset, and under the Schedule Refresh tab, you can:

• Enable scheduled refresh and set refresh frequency (daily, weekly).
• Set preferred time zones and exact refresh times.
• Enter and validate credentials for data sources.
• Enable failure notifications for refresh issues.

9. What is the difference between a calculated column and a measure in Power BI?

Query folding is the process by which Power Query transformations are translated into native queries that are executed by the data source rather than within Power BI. This helps optimize performance by pushing computations to the source system, reducing data transfer and load times. Query folding is more effective with relational databases and can break if unsupported transformations are applied. Maintaining query folding ensures efficient data refresh and optimized performance.

12. Explain the purpose of the Power Query Editor.

Power Query Editor is a data transformation tool within Power BI Desktop that enables users to clean, shape, and combine data from multiple sources before loading it into the data model. It supports a wide variety of transformations such as removing rows/columns, pivoting data, merging tables, and changing data types. Power Query uses the M language under the hood and ensures repeatable and automated ETL workflows.

13. How can you handle performance optimization in Power BI reports?

• Reduce the number of visuals per report page.
• Use measures instead of calculated columns where possible.
• Avoid excessive use of slicers and filters.
• Enable data reduction techniques like aggregations and summarization.
• Use star schema for optimal modeling performance.

14. What is the difference between Power BI Pro and Power BI Premium?

• Power BI Pro: Offers individual licenses for content sharing and collaboration, real-time dashboards, and scheduled refreshes with a limit of 8 refreshes per day.
• Power BI Premium: Offers dedicated cloud capacity, higher dataset size (up to 400GB), up to 48 refreshes per day, and features like paginated reports, AI capabilities, and on-premises reporting with Power BI Report Server.

15. What are KPIs in Power BI and how do you create one?

KPIs (Key Performance Indicators) in Power BI help visualize how well a company is achieving its key business objectives. They typically consist of:

• Actual value: A current metric (e.g., Sales).
• Target value: A goal to reach (e.g., Budgeted Sales).
• Trend: Shows historical data over time.
  To create a KPI, use a KPI visual and configure it by assigning the value, target, and trend fields from your data model.

16. How do bookmarks work in Power BI?

• Capture a specific report view (e.g., filters, visuals, slicers).
• Create bookmarks via the View > Bookmarks Pane.
• Use bookmarks for navigation, storytelling, and toggling visuals.
• Combine with buttons for user-friendly interactive dashboards.
• Bookmarks can save selections, visual states, and drill paths.

17. What is the use of tooltips in Power BI?

• Tooltips provide contextual information when hovering over visuals.
• They can display metrics, comparisons, or summaries.
• Custom tooltips can be created as report pages.
• Enhance user experience and data understanding.
• Useful in dense dashboards with limited space.

18. Explain the importance of data lineage in Power BI.

Data lineage provides a visual map of how data flows from source systems through transformations to the final report visuals. It is essential for:

• Debugging errors in data pipelines.
• Tracking data origins and understanding dependencies.
• Ensuring data integrity across the report lifecycle.
• Collaboration and governance, especially in large enterprises.
• Power BI Service offers lineage views within workspaces.

19. What is a semantic model in Power BI?

A semantic model defines how users interpret and analyze the data. It includes relationships, hierarchies, calculated fields, and metadata. It transforms raw data into user-friendly structures using naming conventions, formatting, and business logic. Power BI uses this model to create self-service analytics experiences, ensuring consistency and ease of use across the organization.

20. What is a hierarchy in Power BI and how is it used?

A hierarchy in Power BI is a structured arrangement of fields that define levels of data granularity.
For example, a Date Hierarchy might include Year → Quarter → Month → Day.
It enables drill-down capabilities in visuals for in-depth analysis.
Hierarchies simplify report creation by combining multiple fields into one structure.
They enhance navigation and user interaction in reports.

21. How can you use drill-down and drill-through features in Power BI?

• Drill-down: Allows users to click a visual and move to a more detailed level (e.g., Year → Quarter → Month).
• Drill-through: Enables navigation to a detailed report page based on a selected item (e.g., click a product to see its detailed sales).
• Enhances interactivity and layered data exploration.
• Requires hierarchies and proper relationships.
• Supports context-based storytelling in reports.

22. What are aggregations in Power BI and why are they useful?

Aggregations are summarized versions of detailed data (e.g., sum of sales by region) that improve performance in large models. Power BI can detect and use these aggregations to respond to queries faster. You can define automatic or manual aggregations in the model. They help in optimizing memory usage and reducing query time for large datasets.

23. How can you share a Power BI report with external users?

You can share reports with external users by using Power BI Pro licenses and inviting them by email.
Ensure the external user also has a Power BI Pro license.
Use Azure B2B or enable Guest Access via Azure Active Directory.
Reports can also be embedded in secure portals or websites.
Proper permissions and RLS rules should be configured for secure sharing.

24. How does Power BI support data governance and security?

Power BI includes several features to support data governance:

• Row-Level Security (RLS)
• Sensitivity Labels (via Microsoft Purview)
• Audit logs and activity monitoring
• Data certification and endorsement
• Integration with Azure AD for identity and access control

25. What steps should you follow for publishing a report in Power BI?

1. Develop the report in Power BI Desktop.
2. Click Publish and sign into Power BI Service.
3. Choose the destination workspace.
4. Set up data refresh schedules and credentials.
5. Share the report or embed it into apps/dashboards.