1. What is Power BI and why is it important for business intelligence?
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Power BI is a Microsoft tool for data visualization and business analytics that transforms raw data into interactive dashboards and reports. It simplifies collecting data from multiple sources, analyzing it quickly, and sharing insights, helping businesses track trends, monitor performance, and make informed decisions. Its intuitive interface and integration with Microsoft tools make it a key asset for business intelligence.
2. How do you connect Power BI to different data sources?
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Power BI can connect to various sources such as databases, Excel files, cloud services, and web APIs. Using the Get Data feature in Power BI Desktop, users select the source, provide credentials, and establish the connection. Data can then be imported into Power BI or accessed live, offering flexibility for different analytical needs.
3. What is the difference between Power Query and DAX in Power BI?
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Power Query is used to extract, clean, and transform data before loading it into the model it’s the data preparation stage. DAX (Data Analysis Expressions) is a formula language used within the data model for calculations and dynamic aggregations. Essentially, Power Query shapes your data upfront, while DAX analyzes it inside reports.
4. What are calculated columns and measures, and when should they be used?
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Calculated columns create new data fields row by row and are stored in the model, useful for adding static data points. Measures are dynamic calculations evaluated on the fly, often used for summaries like totals or averages. Use calculated columns for static, row-level data, and measures for dynamic aggregations that respond to filters and slicers.
5. How do you implement row-level security (RLS) in Power BI?
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RLS restricts data access so users see only what they are allowed to. In Power BI Desktop, define roles and set table filters. After publishing to Power BI Service, assign users or groups to these roles. This ensures secure, role-based access and personalized reporting.
6. What are the ways to refresh data in Power BI?
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Data can be refreshed manually or automatically. Scheduled refreshes keep datasets up to date, while gateways enable refresh for on-premises sources. Full refresh reloads all data, whereas incremental refresh updates only new or changed records, improving efficiency for large datasets.
7. How can you improve Power BI report performance?
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Enhance performance by reducing the data model size, removing unnecessary columns, simplifying complex DAX formulas, and using aggregations. Limiting visuals per page and enabling query folding in Power Query, which pushes transformations to the data source, also speeds up report loading.
8. What are bookmarks in Power BI and how are they useful?
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Bookmarks capture a report page’s current state, including filters, slicers, and visuals. They allow interactive storytelling, guiding users through different scenarios or views. Combined with buttons and navigation, bookmarks make reports more dynamic and engaging.
9. What is the difference between DirectQuery and Import modes in Power BI?
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Import mode loads data into Power BI for fast querying and offline use but requires refreshes. DirectQuery queries data live from the source for real-time results but may be slower. The choice depends on data size, performance needs, and freshness requirements.
10. How do you manage relationships between tables in Power BI?
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Relationships connect tables to build a unified data model. Define them by matching columns (keys) across tables. Proper management, including cardinality, cross-filter direction, and inactive relationships, ensures accurate data flow in visuals and calculations for reliable analysis.