Union and join basics in Tableau - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a union of two tables named Sales2023 and Sales2024.

Tableau

UNION([1], Sales2024)

Drag options to blanks, or click blank then click option'

ASales2023

BJOIN

CMERGE

DAPPEND

Attempts:

3 left

💡 Hint

Common Mistakes

Using JOIN instead of UNION

Using MERGE which is not a Tableau function

Using APPEND which is not a Tableau function

The UNION function combines rows from two tables. Here, Sales2023 is the first table to union with Sales2024.

2fill in blank

medium

Complete the code to join Customers and Orders tables on CustomerID.

Tableau

JOIN Customers ON Customers.CustomerID = [1].CustomerID

Drag options to blanks, or click blank then click option'

AOrders

BEmployees

CProducts

DSales

Attempts:

3 left

💡 Hint

Common Mistakes

Joining Customers with Sales instead of Orders

Using Products or Employees tables incorrectly

The JOIN is between Customers and Orders tables using the CustomerID field from Orders.

3fill in blank

hard

Fix the error in the join condition to correctly join Products and Categories on CategoryID.

Tableau

JOIN Products ON Products.CategoryID = [1].CategoryID

Drag options to blanks, or click blank then click option'

ACustomers

BSales

COrders

DCategories

Attempts:

3 left

💡 Hint

Common Mistakes

Using Sales or Orders instead of Categories

Joining on wrong fields

The join should be between Products and Categories tables on the CategoryID field.

4fill in blank

hard

Fill both blanks to create a left join between Employees and Departments on DepartmentID.

Tableau

LEFT JOIN [1] ON Employees.DepartmentID = [2].DepartmentID

Drag options to blanks, or click blank then click option'

ADepartments

BEmployees

CProjects

DTasks

Attempts:

3 left

💡 Hint

Common Mistakes

Using Employees or other tables instead of Departments

Mixing table names in join condition

We join Employees with Departments on DepartmentID. Both blanks refer to Departments table.

5fill in blank

hard

Fill all three blanks to create an inner join between Orders and Customers on CustomerID and select CustomerName.

Tableau

SELECT [1] FROM Orders JOIN [2] ON Orders.CustomerID = [3].CustomerID

Drag options to blanks, or click blank then click option'

ACustomerName

BCustomers

DOrderDate

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting wrong fields like OrderDate

Joining with wrong tables

Using inconsistent table aliases

The SELECT clause chooses CustomerName. The join is between Orders and Customers on CustomerID.

Practice

1. Which of the following best describes a Union in Tableau?

easy

A. It filters data based on a condition.

B. It combines columns from two tables based on matching keys.

C. It creates a new calculated field.

D. It stacks rows from two or more tables with similar columns.

Solution

1. Step 1: Understand Union purpose

   A Union stacks rows from tables that have the same columns, combining data vertically.

2. Step 2: Compare with Join

   Join combines columns horizontally based on matching keys, not stacking rows.

3. Final Answer:

   It stacks rows from two or more tables with similar columns. -> Option D

4. Quick Check:

   Union = stacking rows [OK]

Hint: Union stacks rows; Join combines columns [OK]

Common Mistakes:

• Confusing Union with Join
• Thinking Union combines columns
• Assuming Union filters data

2. Which syntax correctly represents a Join in Tableau's data source page?

easy

A. Drag one table onto another and select the join type.

B. Use the UNION keyword in the data pane.

C. Create a calculated field with JOIN() function.

D. Right-click a table and select 'Append'.

Solution

1. Step 1: Identify Join method in Tableau

   In Tableau, you join tables by dragging one table onto another and choosing the join type (Inner, Left, Right, Full).

2. Step 2: Eliminate incorrect options

   Union keyword is for unions, JOIN() function does not exist, and 'Append' is not a Tableau option.

3. Final Answer:

   Drag one table onto another and select the join type. -> Option A

4. Quick Check:

   Join = drag tables + select join [OK]

Hint: Join by dragging tables together in Tableau [OK]

Common Mistakes:

• Confusing Union keyword with Join
• Looking for JOIN() function which doesn't exist
• Using 'Append' instead of Union or Join

3. Given two tables:
Table A: ID, Name
Table B: ID, Sales
What will be the result of an Inner Join on ID?

medium

A. A table with only IDs from Table A and no Sales column.

B. A table stacking all rows from both tables vertically.

C. A table with columns ID, Name, Sales containing only matching IDs.

D. A table with all IDs from both tables, including unmatched rows.

Solution

1. Step 1: Understand Inner Join behavior

   Inner Join returns rows where the join key (ID) exists in both tables, combining columns.

2. Step 2: Analyze columns and rows

   The result will have columns ID, Name, Sales and only rows with matching IDs in both tables.

3. Final Answer:

   A table with columns ID, Name, Sales containing only matching IDs. -> Option C

4. Quick Check:

   Inner Join = matching rows + combined columns [OK]

Hint: Inner Join keeps only matching keys with all columns [OK]

Common Mistakes:

• Thinking Inner Join stacks rows
• Expecting unmatched rows included
• Confusing columns included in result

4. You tried to Union two tables but got an error. What is the most likely cause?

medium

A. You forgot to select a join type.

B. The tables have different column names or data types.

C. You used a calculated field instead of a table.

D. You dragged tables instead of using the Union option.

Solution

1. Step 1: Identify Union requirements

   Union requires tables to have matching column names and compatible data types to stack rows.

2. Step 2: Understand error cause

   If columns differ in name or type, Tableau cannot stack rows, causing an error.

3. Final Answer:

   The tables have different column names or data types. -> Option B

4. Quick Check:

   Union error = mismatched columns/types [OK]

Hint: Union needs matching columns and types [OK]

Common Mistakes:

• Confusing Union errors with Join errors
• Not checking column names and types
• Trying to drag tables instead of using Union

5. You have monthly sales data split into two tables: Sales_Jan and Sales_Feb with identical columns. You also have a Customers table with customer details. How do you create a combined dataset showing all sales with customer info?

hard

A. Union Sales_Jan and Sales_Feb, then Join the result with Customers on CustomerID.

B. Join Sales_Jan with Customers, then Union with Sales_Feb.

C. Union Customers with Sales_Jan and Sales_Feb directly.

D. Join Sales_Jan and Sales_Feb on CustomerID, then Union with Customers.

Solution

1. Step 1: Combine monthly sales data vertically

   Since Sales_Jan and Sales_Feb have identical columns, use Union to stack their rows into one sales table.

2. Step 2: Enrich sales data with customer info

   Join the combined sales table with Customers on CustomerID to add customer details horizontally.

3. Final Answer:

   Union Sales_Jan and Sales_Feb, then Join the result with Customers on CustomerID. -> Option A

4. Quick Check:

   Union sales first, then Join customers [OK]

Hint: Union similar tables first, then Join related tables [OK]

Common Mistakes:

• Joining before unioning sales tables
• Trying to union unrelated tables
• Joining sales tables instead of unioning