Blending data sources in Tableau - Step-by-Step Guide

Introduction

Blending data sources in Tableau lets you combine data from different places without merging them into one file. This helps when you want to compare or analyze data that lives separately, like sales numbers and customer info from different systems.

When your sales data is in one database and customer feedback is in another, and you want to see them together.

When you have monthly sales in Excel and yearly targets in a cloud database and want to compare them.

When you want to create a dashboard that shows product inventory from one system and shipping data from another.

When you need to analyze marketing campaign results stored in one source with website traffic data in another.

When you want to avoid copying or merging large datasets but still want combined insights.

Steps

Step 1: Connect to your primary data source

- Data pane

Primary data source appears in the Data pane with its fields listed

Step 2: Connect to your secondary data source

- Data pane

Secondary data source appears below the primary source in the Data pane

Step 3: Drag a field from the primary data source to Rows or Columns shelf

- Worksheet view

Tableau creates a view using the primary data source

Step 4: Drag a related field from the secondary data source to the view

- Data pane

A link icon appears next to the secondary data source, indicating blending is active; data from both sources combine in the view

Step 5: Click the link icon next to the secondary data source

- Data pane

Blending fields are shown; you can add or remove linking fields to control how data blends

Step 6: Adjust the linking fields if needed

- Data pane blending options

The view updates to reflect the new blend relationship

Before vs After

Before

Only data from the primary source is visible in the worksheet, showing sales by region

After

Sales by region from the primary source combined with customer satisfaction scores from the secondary source appear in the worksheet

Settings Reference

Linking Fields

📍 Data pane next to secondary data source

Defines which fields Tableau uses to match data between sources

Default: Automatically linked by common field names

Primary vs Secondary Data Source

📍 Data pane order and icon

Determines which data source drives the view and which blends in

Default: First connected data source is primary

Common Mistakes

Not linking fields correctly between data sources

Tableau cannot match data rows properly, so the blended data shows incorrect or missing values

Ensure the linking fields have the same data type and matching values in both sources

Using blending when a join would be better

Blending is slower and less flexible for detailed row-level combinations

Use data joins in Tableau Prep or the data source if you need detailed combined rows

Summary

Blending data sources lets you combine data from different places without merging files.

You set one data source as primary and link fields to a secondary source to blend data.

Make sure linking fields match well to get accurate combined results.

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