Union and join basics in Tableau - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the difference between Union and Join

Which statement best describes the difference between a Union and a Join in Tableau?

A A Union combines tables horizontally by matching columns; a Join stacks tables vertically by adding rows.

B A Union stacks data tables vertically, adding rows; a Join combines tables horizontally, adding columns based on matching keys.

C Both Union and Join stack tables vertically but differ in how they handle duplicates.

D A Union merges tables by matching keys; a Join appends tables without matching.

💡 Hint

Think about whether you are adding rows or columns when combining tables.

In Tableau, a Union appends tables vertically, adding rows from each table. A Join combines tables horizontally by matching rows based on key columns, adding columns.

🧠 Conceptual

intermediate

Result of a Left Join in Tableau

Given two tables in Tableau: Customers with 5 rows and Orders with 10 rows, where 3 customers have orders, what is the number of rows after a Left Join of Customers to Orders?

A 5 rows

B 10 rows

C 15 rows

D 3 rows

💡 Hint

Remember, a Left Join keeps all rows from the left table.

A Left Join keeps all rows from the left table (Customers). Since Customers has 5 rows, the result will have 5 rows, with matching Orders data where available.

❓ visualization

advanced

Visualizing the effect of a Union

You have two tables with sales data for two different years. You perform a Union in Tableau. Which visualization best shows the combined sales over both years?

A A bar chart comparing sales side by side for each year without combining data.

B A pie chart showing sales distribution by year separately.

C A line chart showing sales over time with data points from both years combined.

D A scatter plot showing sales vs. customers for only one year.

💡 Hint

Think about how a Union stacks data and how to show combined trends.

A Union stacks data vertically, so combining sales from both years allows a line chart over time to show the total sales trend across years.

🔧 Formula Fix

advanced

Troubleshooting a Join with Missing Data

You performed an Inner Join between Products and Sales tables on Product ID, but some expected products are missing in the result. What is the most likely cause?

A Some Product IDs in Products do not match any Product ID in Sales, so those rows are excluded.

B The Product ID columns have different data types causing the Join to fail completely.

C The Join type should be changed to Left Join to include all Sales rows.

D The Union was used instead of Join, causing missing rows.

💡 Hint

Consider how Inner Join works with matching keys.

An Inner Join returns only rows with matching keys in both tables. If some Product IDs in Products don't exist in Sales, those rows are excluded, causing missing products.

🎯 Scenario

expert

Choosing the Right Combination Method for Data Integration

Your company has two separate Excel files: one with customer contact info and another with customer purchase history. You want to create a Tableau dashboard showing all customers with their purchase totals. Which method should you use to combine these files?

A Use a Union to stack the two tables vertically since they have different columns.

B Append the purchase history file to the contact info file manually before importing.

C Import both files separately and blend the data in Tableau without joining.

D Use a Join on Customer ID to combine contact info and purchase history horizontally.

💡 Hint

Think about how to combine related data with matching keys.

Joining on Customer ID combines contact info and purchase history horizontally, allowing analysis of customers with their purchase totals in one table.