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Power BI Interview Question and Answer

Introduction

In today's data-driven world, Power BI has emerged as a pivotal tool for organizations seeking to harness the power of their data. As more and more businesses adopt this robust data visualization and business intelligence platform, the demand for skilled Power BI professionals is soaring.

Are you gearing up for a Power BI job interview or simply looking to bolster your understanding of this dynamic tool? You're in the right place. In this article, we'll explore a comprehensive set of Power BI interview questions that will not only help you prepare effectively but also empower you to showcase your expertise confidently. Whether you're a seasoned Power BI pro or just starting your journey, these questions and answers will be your secret weapon to excel in Power BI interviews. So, let's dive into the world of Power BI and prepare for your next career move.

What are the key components of Power BI?

  • Power BI Desktop - Used to create reports and data models. Allows data cleaning, shaping, and modeling.
  • Power BI Service - Cloud service to collaborate on Power BI apps and dashboards. Provides sharing and publication capabilities.
  • Power BI Mobile Apps - To view and interact with Power BI dashboards on mobile devices.
  • Power BI Gateway - Enables refresh of on-premises data sources. Provides security when connecting to on-prem sources.

What are the differences between Power BI Desktop and Power BI Service?

Power BI Desktop is used for report creation, data modeling, and data preparation. Power BI Service is used to publish and share interactive reports and collaborate with others. Key difference.

Desktop

  • Report design, authoring
  • Data modeling, shaping, ETL
  • Visualization design

Service

  • Centralized publishing
  • Dashboard and app sharing
  • Access control and security
  • Collaboration
  • Mobile apps
  • Analyze in Excel
  • AI insights
  • Push data sets and reports

How does Power BI optimize query performance?

Power BI uses several techniques to optimize query performance.

  • Incremental data refresh only loads new or modified data instead of full loads every time.
  • Query reduction removes duplicate and similar queries and reuses the cached results.
  • Query compression reduces query size and minimizes resource utilization.
  • VertiPaq engine uses in-memory caching and compression, which improves performance.
  • DirectQuery can connect live to data sources without data import.
  • DAX computation is optimized to handle large data volumes.

What is DAX in Power BI? Give examples of DAX functions.

DAX stands for Data Analysis Expressions. It is a formula expression language for creating custom calculations and logic in Power BI. Some examples of DAX functions:

  • CALCULATE: Overrides context and creates new filter contexts.
  • SUM: Totals the values in a column. SUM(Sales[Revenue])
  • AVERAGE: Calculates the average of a numeric column. AVERAGE(Sales[Revenue])
  • MIN, MAX: Returns min or max from a column. MIN(Sales[Revenue])
  • COUNTROWS: Counts the number of rows in a table. COUNTROWS(Sales)
  • DATEADD: Adds a number of time units to a date. DATEADD(Sales[Date], -30, DAY)

How can you optimize DAX query performance in Power BI?

Some ways to optimize DAX query performance.

  • Use CALCULATE instead of long filters to change the context.
  • Limit nested iterations by restructuring the formula.
  • Use SUMX instead of ADDCOLUMNS/SUMMARIZE for aggregation.
  • Make sure the columns used in DAX have proper relationships.
  • Use userelationship vs. crossfilter in DAX to optimize aggregations.
  • Add indexes on columns used in DAX calculations.
  • Use variables and reuse DAX expressions instead of repeating code.

What are the steps to create a simple report in Power BI Desktop?

Steps to create a simple report.

  • Connect to a data source
  • Load the data into Power BI
  • Shape and transform the data as needed
  • Create relationships between tables
  • Design the report layout - add titles, tables, charts, and filters
  • Develop any required DAX calculations
  • Add formatting, colors, and images as needed
  • Publish the report to the Power BI service to share

How can you optimize a Power BI data model?

Optimization techniques for Power BI data model.

  • Design tables around business processes and minimize table duplication
  • Create proper relationships between tables
  • Normalize data to remove redundancies and inconsistencies
  • Add indexes on columns used in relationships, keys, aggregations
  • Summarize and aggregate data during the ETL process before import
  • Import only columns and data needed for reporting
  • Compress tables using column formatting and summarization

What are some best practices for designing a Power BI report?

Some Power BI report design best practices.

  • Focus visuals on key metrics, insights, and actions
  • Limit visuals to key facts and overview data. Drill down for details
  • Use themes and consistent layouts across multiple pages
  • Optimize visual types based on data being displayed
  • Format visuals consistently using alignment, colors, fonts, etc
  • Ensure visualizations are simple and easy to interpret
  • Make effective use of white space and avoid clutter
  • Test reports on mobile layouts
  • Add explanatory titles, legends, tooltips

How can you secure data in Power BI?

  • Row Level Security can restrict data access at the row level based on filters.
  • Object-level security can be defined via roles to limit access to reports.
  • Enable Data Encryption at rest and in transit.
  • Mask or anonymize sensitive data before sharing datasets.
  • Incremental refresh can limit the exposure of full data to the service.
  • Enable SSAS and Import mode to retain data on-premises.
  • Restrict Power BI access to permitted users only.
  • Utilize read-only sharing whenever possible.

What are some tips for creating effective Power BI dashboards?

  • Focus on key metrics and KPIs relevant to the audience.
  • Limit to essential visualizations, and remove clutter.
  • Use Q&A for quick ad-hoc analyses.
  • Enable drill down from overview to details.
  • Use consistent layouts, colors, and formatting.
  • Optimize for quick load speed and interaction.
  • Make the dashboard easy to interpret at a glance.
  • Refresh datasets and data models frequently.
  • Follow responsive design principles.
  • Test on mobile layouts.

How can you embed Power BI reports into an application?

To embed Power BI into an application.

  • Use Power BI Embedded to integrate reports into your app using JavaScript or .NET SDK.
  • Utilize Power BI Embedded Azure capacity for dedicated resource allocation.
  • Call Power BI REST APIs from your app to retrieve data and definitions.
  • Use Embed tokens to securely embed reports, changing tokens periodically.
  • Implement Row Level Security to restrict data access.
  • Handle licensing appropriately, either pay-per-user or Power BI Premium.

What are the licensing options available for Power BI?

  • Power BI Free - Limited functionality, individual use only
  • Power BI Pro - Full capabilities for individuals, $9.99 per user monthly
  • Power BI Premium - Dedicated resources, user flexibility, pricing by cores
  • Power BI Embedded - Embed reports into an application, pay-per-render
  • Power BI Report Server - On-prem reporting with Premium capacity

Can you use DAX and M functions in Power BI? What is the difference between them?

Yes, both DAX and M can be used in Power BI.

DAX is a formula language for creating custom calculations and measures. M is the Power Query formula language used for data transformations like joining, appending queries, adding columns, etc.

Key differences

  • DAX formulas operate on the entire table vs. row by row for M.
  • DAX is computed during query runtime vs. import stage for M.
  • DAX uses relationships between tables, while M focuses on shaping individual tables.

How can you improve the performance of Power BI dashboards?

  • Simplify visualizations and remove unnecessary complexities.
  • Apply filters and limitations to fetch only required data.
  • Optimize DAX measures to avoid heavy computations.
  • Import only essential data to the dataset, and minimize query rows.
  • Use aggregate and summarized tables to reduce model size.
  • Refresh datasets during off-peak hours to reduce load.
  • Set up row-level security correctly to avoid slow filters.
  • Use DirectQuery for live connections instead of Refresh.
  • Allocate sufficient Premium capacity for complex data models.

What is a paginated report in Power BI, and when would you use it?

Paginated reports in Power BI allow printing large reports in a readable format vs. interactive reports. Key features.

  • Designed for structured data sources like SSRS, databases
  • Optimized printing layout with headers, footers, page numbers, etc
  • Parameters, filters, and actions can be embedded
  • Exported to PDF, Word, Excel, and PowerPoint formats
  • Integrated with Power BI dashboards and service

Use cases. financial statements, operational reports, archival of reports, proposals, etc.

How can you monitor dataset refresh errors in Power BI?

Methods to monitor dataset refresh errors.

  • Refresh history displays previous refresh attempts and results.
  • Configure refresh error email notifications.
  • Set up monitoring with Power BI alert rules.
  • Check refresh errors using PowerShell cmdlets.
  • Log refresh errors to Azure Event Hub or Azure Log Analytics.
  • Handle refresh errors in the script using the Partial Errors option.
  • Review refresh utilization under Usage metrics.
  • Configure failure notifications for scheduled refreshes.

How does Power BI handle security for data sources and user access?

Power BI has several security mechanisms.

  • Row Level Security (RLS) filters data rows users can access through DAX expressions. Can filter at table or model level.
  • Object Level Security (OLS) secures reports/dashboards by configuring access through workspace roles.
  • Data encryption is at rest and in transit through AES-256-bit encryption.
  • On-premises data gateway acts as a secure bridge to on-prem sources. Encrypts credentials.
  • Restrict access to cloud resources like app insights and storage accounts hosting PBIX files.
  • Behind VNet, a firewall to limit external access.

What are some strategies for optimizing large Power BI data models?

Strategies for optimizing large Power BI models.

  • Carefully structure tables to avoid duplications. Use unique identifiers.
  • Add indexes on related columns, relationships, keys, and aggregates.
  • Partition the model into sections isolating unrelated data.
  • Aggregate and summarize data before importing.
  • Column formatting is like categories for compression.
  • Hide unused columns. Disable query reduction if incorrectly minimizing queries.
  • Incremental refresh only loads new data.
  • DirectQuery for live connections to avoid import.
  • Simplify DAX expressions by removing iterators and duplications.

How would you migrate an on-premises SSAS Tabular model to Power BI Premium?

Steps to migrate SSAS Tabular to Power BI Premium.

  • Take inventory of data sources, security roles, and reports/dimensions.
  • Assess dataset size and required Premium capacity.
  • Determine DAX calculation approach - reuse vs. rewrite from SSAS model.
  • Plan gateway configuration for on-prem data sources.
  • Develop a testing strategy and rollback plan.
  • Set up RLS rules to handle security.
  • Migrate reports/visualizations using Power BI Desktop.
  • Validate data parity and test extensively before go-live.
  • Decommission SSAS instance after cutover.
  • Manage communications and training for users.

You need to build a mission-critical dashboard with a 99.9% uptime requirement. How would you architect this on Power BI?

For a highly available Power BI dashboard

  • Have a Premium capacity for dedicated resources. Autoscaling enabled.
  • Host Power BI report server on AlwaysOn Availability Groups SQL Cluster for HA.
  • Load balancer to distribute requests across Report Servers.
  • Scale-out horizontally by adding more Report Server instances.
  • On-premises data gateways in a failover cluster.
  • Schedule caching during non-peak hours.
  • Implement redundancy for data sources.
  • Set up monitoring and alerts to proactively respond.
  • Plan manual failover process for gateway.
  • Handle failback and syncing of caches across nodes.
  • Define SLA, metrics monitoring, and regular disaster recovery drills.

How can you enable detailed audit logging and analytics for Power BI usage?

For Power BI auditing and usage analytics:

  • Send logs like a gateway. The tenant logs to the Log Analytics workspace.
  • Utilize PowerShell commands to extract admin logs, usage metrics, etc.
  • Power BI activity log API provides access to operational data.
  • Build custom dashboards on activity data streamed to Azure Data Explorer.
  • Integrate Power BI App Insights analytics into the external logging system.
  • Capture dataset refresh metrics and errors.
  • Log access attempts and unauthorized operations centrally.
  • Analyze usage trends on reports and dashboards.
  • Monitor dataflow, dataset failures, and bottlenecks.
  • Correlate logs with security systems like Azure Sentinel.

How can you optimize the performance of DirectQuery in Power BI?

  • Carefully test and validate query performance on the source database. Tune queries.
  • Ensure proper indexes on related columns, aggregates, etc., in the source DB.
  • Limit the number of visuals on a page querying the source database.
  • Apply filters to restrict the rows fetched from the database.
  • Use aggregate tables, if possible, instead of entity tables. Pre-summarize data.
  • Import some static data into the model to avoid hitting the source frequently.
  • Allocate sufficient Premium capacity for concurrency.
  • Route queries efficiently if the source database is in a different network.
  • Disable query reduction if causing unnecessary queries to the source.
  • Optimize DAX measures to avoid expensive iterative functions.

What are some effective strategies for troubleshooting performance issues in Power BI?

Performance troubleshooting strategies.

  • Review query traces to identify long-running DAX and M queries.
  • Use SQL Server Profiler for insights into DAX query plans.
  • Analyze critical path - where time is spent - import, DAX calculation, visual rendering.
  • Look for measures causing complex iterative calculations. Simplify expressions.
  • Identify poorly optimized relationships performing slow merges and joins.
  • Check for bloated tables that need better compression.
  • Analyze demand and capacity planning - scale Premium capacity if needed.
  • Drill down on visuals causing complexity due to too many fields/filters. Simplify.
  • Partition models into smaller sections if the single model is slow.
  • Check load on gateways, and scale out if bottlenecks.

How would you migrate a large on-premises SSAS Tabular model to Azure Analysis Services?

To migrate SSAS Tabular to Azure Analysis Services.

  • Take inventory of data sources, roles, reports, and dimensions.
  • Assess the required service tier based on model size and query volumes.
  • Set up data gateways to existing data sources. Reuse connections.
  • Script out the model using SSMS and import DAX and table schemas to the new AAS instance.
  • Recreate roles and RLS rules in AAS.
  • Migrate reports and clients to point to the new AAS endpoint.
  • Validate data parity between models.
  • Gradually divert traffic from SSAS to AAS instance.
  • Decommission on-prem SSAS once the migration is complete.
  • Configure monitoring and alerting for AAS instances.
  • Plan rollback in case of issues during migration.

You have been asked to select a Power BI solution for your organization. What are the key factors you would consider?

Key factors to consider when selecting a Power BI solution:

  • Requirements around data volumes, complexity, and user access needs.
  • Data sources - cloud vs. on-premises vs. hybrid.
  • Scalability needs in the future.
  • Usage patterns - ad-hoc vs. standardized dashboards.
  • Premium capacity requirements - size, regions.
  • Security, compliance, and data residency needs.
  • Lifecycle management needs on reports and dashboards.
  • Training and support needs.
  • Integration needs with applications, portals, and databases.
  • Cost analysis between solutions - Pro vs. Premium vs. Embedded.
  • Resource skillsets available and need for consultants.

How can you optimize Paginated Reports in Power BI for performance?

To optimize Power BI Paginated Report performance:

  • Simplify layout complexity and visualizations.
  • Filter dataset to only required rows.
  • Use aggregates vs. base tables. Pre-summarize data.
  • Optimize DAX measures by removing iterators.
  • Format columns like dates to compressed data types.
  • Import smaller chunks of data using page breaks and page filters.
  • Allocate sufficient Premium capacity.
  • Minimize access to irrelevant model partitions.
  • Enable and tune cache refresh for datasets.
  • Schedule report generation during low usage hours.


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