✅ 🚀 Power BI Interview Questions (For Analyst/BI Roles)

1️⃣ Explain DAX CALCULATE() Function
Used to modify the filter context of a measure.
✅ Example:
CALCULATE(SUM(Sales[Amount]), Region = "West")

2️⃣ What is ALL() function in DAX?
Removes filters — useful for calculating totals regardless of filters.

3️⃣ How does FILTER() differ from CALCULATE()?
FILTER returns a table; CALCULATE modifies context using that table.

4️⃣ Difference between SUMX and SUM?
SUMX iterates over rows, applying an expression; SUM just totals a column.

5️⃣ Explain STAR vs SNOWFLAKE Schema
- Star: denormalized, simple
- Snowflake: normalized, complex relationships

6️⃣ What is a Composite Model?
Allows combining Import + DirectQuery sources in one report.

7️⃣ What are Virtual Tables in DAX?
Tables created in memory during calculation — not physical.

8️⃣ What is the difference between USERNAME() and USERPRINCIPALNAME()?
Used for dynamic RLS.
- USERNAME(): Local machine login
- USERPRINCIPALNAME(): Cloud identity (email)

9️⃣ Explain Time Intelligence Functions
Examples:
- TOTALYTD(), DATESINPERIOD(), SAMEPERIODLASTYEAR()
Used for date-based calculations.

🔟 Common DAX Optimization Tips
- Avoid complex nested functions
- Use variables (VAR)
- Reduce row context with calculated columns

1️⃣1️⃣ What is Incremental Refresh?
Only refreshes new/changed data – improves performance in large datasets.

1️⃣2️⃣ What are Parameters in Power BI?
User-defined inputs to make reports dynamic and reusable.

1️⃣3️⃣ What is a Dataflow?
Reusable ETL layer in Power BI Service using Power Query Online.

1️⃣4️⃣ Difference Between Live Connection vs DirectQuery vs Import
- Import: Fast, offline
- DirectQuery: Real-time, slower
- Live Connection: Full model lives on SSAS

1️⃣5️⃣ Advanced Visuals Use Cases
- Decomposition Tree for root cause analysis
- KPI Cards for performance metrics
- Paginated Reports for printable tables

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