Top Tableau Scenario-Based Interview Questions Set -3 (1- 10)

 

1. How would you combine historical and current data?
   Use UNION to append both datasets having same columns.
   Example SQL:

   SELECT * FROM Sales_History
   UNION ALL
   SELECT * FROM Sales_Current
   

   In Tableau, drag one table below another to create union.

2. How would you union monthly files automatically?
   Use Wildcard Union in Tableau for files with similar structure.
   Example:

   Sales_Jan.csv
   Sales_Feb.csv
   Sales_Mar.csv
   

   Use:

   Sales_*.csv
   

   Tableau automatically combines all matching files.

3. How would you handle null values?
   Use IFNULL() or ZN() to replace nulls.
   Example:

   IFNULL([Profit],0)
   

   or

   ZN([Sales])
   

   to convert NULL into 0.

4. How would you replace missing dates in a trend chart?
   Convert date to continuous and enable “Show Missing Values.”
   Example:

   MONTH([Order Date])
   

   Then right-click axis → Show Missing Values.

5. How would you create a complete date scaffold?
   Create a calendar table containing all dates and join with fact table.
   Example SQL:

   SELECT Calendar.Date, Sales.Amount
   FROM Calendar
   LEFT JOIN Sales
   ON Calendar.Date = Sales.OrderDate
   

   This ensures all dates appear even without transactions.

6. How would you show data when no transactions exist?
   Use LEFT JOIN with dimension/scaffold table.
   Example:

   SELECT C.CustomerName, IFNULL(SUM(S.Amount),0)
   FROM Customers C
   LEFT JOIN Sales S
   ON C.CustomerID = S.CustomerID
   GROUP BY C.CustomerName
   

   Customers with no sales still appear.

7. How would you use relationship vs join?
   Use Relationships for logical layer and Joins for physical merge.
   Example:
   • Relationship keeps tables separate until query time.
   • Join physically combines rows immediately using Inner/Left Join.

8. How would you optimize a slow dashboard?
   Reduce marks, avoid unnecessary quick filters, and simplify calculations.
   Example:

   IF SUM([Sales]) > 1000 THEN "High" END
   

   Replace complex nested calculations with simpler logic.

9. How would you improve dashboard load time?
   Use extracts instead of live connection and aggregate data.
   Example:

   SUM([Sales])
   

   at Month level instead of transaction level reduces records processed.

10. How would you improve filter performance?
    Use Context Filters so Tableau processes smaller datasets first.
    Example:

• Add Region filter to Context.
• State filter now works only on selected Region data.

11. How would you optimize heavy LODs?
    Push calculations to database or simplify FIXED calculations.
    Example:

{ FIXED [Customer ID] : SUM([Sales]) }

Instead of multiple nested LODs, pre-aggregate data in SQL/ETL.

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