Blending data sources in Tableau - Dashboard Guide

Dashboard Mode - Blending data sources

Business Question

How can we combine sales data from two different sources to see total sales by product category and region?

Sample Data

Data Source 1: Sales 2023

Order ID	Product Category	Region	Sales Amount
1001	Furniture	East	250
1002	Technology	West	400
1003	Office Supplies	East	150
1004	Furniture	West	300
1005	Technology	East	500

Data Source 2: Sales 2024

Order ID	Product Category	Region	Sales Amount
2001	Furniture	East	350
2002	Technology	West	450
2003	Office Supplies	East	200
2004	Furniture	West	400
2005	Technology	East	550

Dashboard Components

• KPI Card: Total Sales
  Formula: SUM([Sales Amount]) from both data sources blended on Product Category and Region.
  Result: 3650 (sum of all sales amounts from both sources)
• Bar Chart: Sales by Product Category
  Formula: SUM([Sales Amount]) grouped by [Product Category] from blended data.
  Result:
  Furniture: 1300
  Technology: 1900
  Office Supplies: 350
• Map Chart: Sales by Region
  Formula: SUM([Sales Amount]) grouped by [Region] from blended data.
  Result:
  East: 2000
  West: 1650
• Table: Detailed Sales
  Shows Order ID, Product Category, Region, Sales Amount from both sources combined.

Dashboard Layout

+----------------------+-----------------------+
|      KPI Card        |   Bar Chart            |
|  Total Sales: 3650   |  Sales by Product Cat  |
|                      |  Furniture, Tech, etc. |
+----------------------+-----------------------+
|                      Map Chart: Sales by Region |
|                      East, West                 |
+--------------------------------+----------------+
|       Table: Detailed Sales (Order ID, Product, Region, Sales)       |
+---------------------------------------------------------------------+
  

Interactivity

Filters for Product Category and Region apply to all components. Selecting a category or region updates the KPI card, bar chart, map, and table to show only matching blended data.

Self Check

If you add a filter for Region = East, which components update and what changes?

• All components update to show only East region data.
• KPI Card shows total sales for East: 250 + 150 + 500 + 350 + 200 + 550 = 2000.
• Bar Chart shows sales by product category only for East.
• Map Chart highlights East region sales only.
• Table shows only orders from East region.

Key Result

A dashboard blending two sales data sources to show total and detailed sales by product category and region with interactive filters.

Practice

1. What is the main purpose of blending data sources in Tableau?

easy

A. To create a single table by merging all data sources permanently

B. To combine data from different sources using common fields without merging tables

C. To replace the primary data source with a secondary one

D. To export data from Tableau to external databases

Solution

1. Step 1: Understand blending concept

   Blending connects data from different sources using common fields without merging them permanently.

2. Step 2: Compare options

   To combine data from different sources using common fields without merging tables correctly describes blending. Options A, C, and D describe other unrelated actions.

3. Final Answer:

   To combine data from different sources using common fields without merging tables -> Option B

4. Quick Check:

   Blending = combine without merging [OK]

Hint: Blending links data without merging tables [OK]

Common Mistakes:

• Confusing blending with joining or merging tables
• Thinking blending replaces the primary source
• Assuming blending exports data

2. Which of the following is the correct way to identify the linking field in Tableau data blending?

easy

A. The field with a red cross in the primary data source

B. The field with a blue checkmark in the secondary data source

C. The field with a green plus sign in the primary data source

D. The field with an orange chain link icon in the secondary data source

Solution

1. Step 1: Recognize linking field icon

   In Tableau, linking fields in the secondary data source show an orange chain link icon.

2. Step 2: Match options to icons

   The field with an orange chain link icon in the secondary data source correctly identifies the orange chain link icon as the linking field. Other options describe incorrect icons or colors.

3. Final Answer:

   The field with an orange chain link icon in the secondary data source -> Option D

4. Quick Check:

   Linking field = orange chain link icon [OK]

Hint: Look for orange chain link icon for linking fields [OK]

Common Mistakes:

• Confusing linking field icon with checkmarks or plus signs
• Looking for icons in the primary instead of secondary source
• Ignoring icon colors

3. Given two data sources: Primary with fields OrderID, Sales and Secondary with fields OrderID, CustomerName. If you blend on OrderID and create a view showing Sales and CustomerName, what will happen if an OrderID exists only in the secondary source?

medium

A. The view will exclude that OrderID because it is missing in the primary source

B. The view will show Sales as null and CustomerName for that OrderID

C. The view will show Sales and CustomerName as null

D. The view will cause an error and not display

Solution

1. Step 1: Understand primary source control

   In blending, the primary source controls the rows shown. If an OrderID is missing in primary, it won't appear.

2. Step 2: Analyze missing OrderID in primary

   Since the OrderID exists only in secondary, it will be excluded from the view.

3. Final Answer:

   The view will exclude that OrderID because it is missing in the primary source -> Option A

4. Quick Check:

   Primary source controls rows = missing keys excluded [OK]

Hint: Primary source controls rows shown in blending [OK]

Common Mistakes:

• Expecting secondary-only keys to appear in the view
• Thinking null values appear for missing primary keys
• Assuming blending causes errors on missing keys

4. You blended two data sources on CustomerID. However, the secondary data source fields show Null values in your view. What is the most likely cause?

medium

A. You forgot to refresh the data sources

B. The primary data source is missing the CustomerID field

C. The linking field CustomerID has mismatched data types between sources

D. The secondary data source is set as primary by mistake

Solution

1. Step 1: Check linking field compatibility

   Blending requires linking fields to have matching data types to join correctly.

2. Step 2: Identify cause of nulls

   If data types differ, Tableau cannot match keys, causing nulls in secondary fields.

3. Final Answer:

   The linking field CustomerID has mismatched data types between sources -> Option C

4. Quick Check:

   Matching data types needed for linking fields [OK]

Hint: Check data types of linking fields if nulls appear [OK]

Common Mistakes:

• Assuming missing fields cause nulls instead of mismatched types
• Confusing primary and secondary source roles
• Ignoring need to refresh data

5. You have two data sources: SalesData (Primary) with OrderID, SalesAmount and CustomerData (Secondary) with CustomerID, OrderID, Region. You want to create a view showing total sales by region. How should you blend and aggregate the data correctly?

hard

A. Blend on OrderID, use Region from secondary, and create a calculated field summing SalesAmount grouped by Region

B. Blend on CustomerID, use Region from secondary, and sum SalesAmount without grouping

C. Join the two sources on OrderID instead of blending, then sum SalesAmount by Region

D. Blend on Region, then sum SalesAmount grouped by OrderID

Solution

1. Step 1: Identify correct linking field

   OrderID exists in both sources and links sales to customer region.

2. Step 2: Blend on OrderID and aggregate

   Blend on OrderID, use Region from secondary, then sum SalesAmount grouped by Region for total sales by region.

3. Final Answer:

   Blend on OrderID, use Region from secondary, and create a calculated field summing SalesAmount grouped by Region -> Option A

4. Quick Check:

   Blend on OrderID + sum Sales by Region [OK]

Hint: Blend on common key, aggregate sales by region [OK]

Common Mistakes:

• Blending on wrong field like CustomerID or Region
• Not grouping sales by region
• Confusing blending with joining