How to Edit Blend Relationships in Tableau
When you first drag fields from two different data sources into the same Tableau view, a moment of magic happens: your data blends. But sometimes, that magic creates an illusion. Tableau does its best to guess how your two sources relate, usually by matching field names like "Date" or "Region." When it gets that guess wrong, your beautifully designed dashboard will show completely inaccurate results. This article is your guide to taking control of how Tableau blends your data by editing blend relationships manually, so your reports are always telling the truth.
What is Data Blending in Tableau?
Before editing blend relationships, it’s helpful to quickly recap what data blending is and when to use it. At its core, data blending is a way to combine data from separate, distinct data sources and display it in a single visualization. Think of it as a left join on an aggregated level.
For example, you might have:
- Your website traffic data living in Google Analytics.
- Your ad spend data living in a Google Sheet or Excel workbook.
- Your sales and revenue information living in Salesforce.
Each of these is a different data source. If you want to build a report that shows ad spend next to the website sessions and revenue it generated, you need to use data blending. This is different from a join, which you use to combine tables from the same data source (like joining an Orders table and a Customers table from a single eCommerce database).
When you use fields from a second data source, Tableau designates the first source as the primary data source (marked with a blue checkmark) and the second as the secondary data source (marked with an orange checkmark). Data from the secondary source is always aggregated to the level of the linking fields from the primary source.
When Tableau Gets Blending Wrong (and Why It’s Okay)
Tableau's default "Automatic" blending tries to save you time. It scans the field names in both of your data sources. If it sees a field named "Date" in your primary source and another field named "Date" in your secondary source, it logically assumes you want to link them on that common dimension.
This is often a great starting point, but it's rarely the full story. Common issues include:
- Mismatched Field Names: Your primary source might have a field called 'Campaign ID', while your secondary source uses 'Campaign Identifier'. Tableau won’t automatically link these because the names are different, even though they contain the same information.
- Needing Multiple Linking Fields: Your report might need to blend data based on both the 'Date' and the 'Campaign Name' to be accurate. If Tableau only links by 'Date', you’ll see revenue grouped by day, but not by the specific campaigns that drove it.
- Incorrect Automatic Links: Sometimes Tableau links fields that happen to share a name but contain unrelated data, leading to confusing results or no results at all. For example, linking 'ID' in an ad platform table to 'ID' in a customer support ticket table would be meaningless.
When this happens, your dashboard might show incomplete data, repetitive values, or confusing asterisks (*). Seeing an asterisk means Tableau can’t compute a single value because there are multiple potential matches from the secondary data source for a single mark in the primary data source. This is a clear red flag that your blend relationship needs adjusting.
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Step-by-Step Guide: How to Edit Blend Relationships
Let's walk through a common scenario. Imagine you're blending Shopify sales data (primary source) with Facebook Ads spend data from a spreadsheet (secondary source). You want to see daily Sales attributed to each Campaign. Tableau automatically linked the sources using the 'Date' field, but you also need to link them by campaign.
Step 1: Identify the Active Linking Fields
First, add fields from your primary data source (Shopify) to your view. Let’s say you drag your Shopify Date field to Columns and Sales to Rows. This works perfectly fine.
Now, go to your secondary data source (Facebook Ads). You'll notice small chain link icons next to some of the dimensions. A solid gray chain link icon indicates a potential linking field. An orange chain link icon means it is an active linking field for the current worksheet.
After Tableau's automatic blend, you probably see the orange chain link icon only next to 'Date'. If you drag your 'Ad Spend' measure to the view, the numbers will be wrong because the spend isn’t broken down by campaign. Your mission is to make another orange link appear next to the campaign field.
Step 2: Open the Edit Blend Relationships Menu
With an active link in place (like the auto-blended 'Date'), navigating to the editing menu is simple.
From the top menu in your Tableau worksheet, click: Data > Edit Blend Relationships...
This opens a dialog box that serves as the command center for all your data blending rules.
Step 3: Understanding the Edit Relationships Dialog Box
This box can look intimidating, but it's really straightforward once you know what you’re looking at.
- Primary data source: Shows the active primary data source for your current sheet (e.g., Shopify Sales). You can select a different one from the dropdown if needed.
- Secondary data source: Shows the active secondary source (e.g., Facebook Ads Spend).
- Relationships: This is where you do the work. The dialog shows two options:
Below these options, you'll see a list of fields from your secondary data source. If you’re using 'Automatic', you'll see how Tableau has mapped them. Your goal is to create your own mapping.
Step 4: Create a Custom Relationship
This is where you tell Tableau exactly how the two data sources relate.
- Select the Custom radio button. You'll notice the linking fields below are no longer grayed out.
- You now need to add a new connection. Click the Add... button.
- A smaller dialog box for “Add/Edit Field Mapping” will appear. On the left, it shows fields from your primary Shopify source. On the right, it shows fields from your secondary Facebook Ads source.
- From the left dropdown, select your campaign identifier, which might be called something like
Campaign. - From the right dropdown, select the corresponding campaign identifier, which in your spreadsheet might be named
Campaign Name. - Click OK to confirm this new field map.
You will now see your new relationship (Campaign -> Campaign Name) in the list of custom relationships. The 'Date' to 'Date' link might still exist from the automatic setting, which is fine. You can have multiple linking fields.
Step 5: Verify the New Relationship
Click OK to close the Edit Relationships dialog box. Look at your Data pane for the secondary source (Facebook Ads). You should now see the orange chain link icon next to both the Date field and the Campaign Name field.
This confirms that Tableau is now blending data using both dimensions. When you place the Campaign Name field onto the shelf (e.g., on Rows next to Sales), and you have Ad Spend in the view, your data will align correctly. You'll see daily sales and spend for each specific campaign, side-by-side - the accurate report you were aiming for!
Common Scenarios and Troubleshooting Tips
Knowing the steps is great, but real-world data isn't always neat and tidy. Here are some common hurdles and how to clear them.
Scenario 1: Dealing With Different Data Types
Data blending requires the linking fields to have the same data type. You cannot blend a UserID that's a Number in one source with a UserID that's a Text String in another. Tableau won't even show the mismatched field as an option in the Edit Relationships dialog.
To fix this, create a calculated field in one of the sources to change its data type. For example, if UserID is a number, create a new calculated field called 'UserID (String)' with the formula:
STR([UserID])Now, you can use this new dimension with the correct data type to build your custom blend relationship.
Scenario 2: The Dreaded Red Link Icon
Sometimes you’ll build what seems like a perfectly good custom relationship, only to see a broken red chain link icon in the Data pane. A red link means the established relationship is invalid for the current worksheet.
This almost always happens because one of the linking fields is missing from your view (the "shelf"). A core rule of blending is that at least one linking field from the primary source must be active in the worksheet for the blend to work. If you build a sheet and then remove the 'Date' and 'Campaign' pills, the link will break. Simply drag one of the primary source's linking dimensions back onto Rows, Columns, or Detail to fix it and make the red icon turn orange again.
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Scenario 3: Fixing Asterisks in Your View
As mentioned earlier, an asterisk (*) appears in your table when Tableau finds multiple matching values in the secondary source for a single value in the primary source but doesn't know how to aggregate them. For example, you are displaying states, but your blend link is only a date, not a specific state. There is more than one date on any given state, thus, the asterisk appears.
The fix is almost always related to the blend's "level of detail." Go back into Data > Edit Blend Relationships... and ensure you have linked the fields that create a unique identifier for a row. If you're looking at sales by-product, by-store, by-day, you need Product ID, Store ID, and Date as your linking fields. Adding the missing dimension to your relationship will typically resolve the asterisk issue.
Final Thoughts
Mastering how to edit blend relationships is what separates a novice Tableau user from a proficient one. It grants you the precision to connect disparate data sources confidently, ensuring your dashboards are not just visually appealing but also factually sound and truly insightful. By taking direct control over these connections, you can build powerful, unified views of your business performance that weren’t possible otherwise.
The process of connecting data sources and defining these relationships helps you gain deep insights, but it can also be a manual and often time-consuming step - especially when you’re pulling sales, marketing, and operational data from half a dozen different platforms. That’s why we created a tool to automate this process. With Graphed, you can securely connect all your sources in one place, and instead of manually editing blend relationships, you can just ask questions in plain English like "Create a dashboard showing Shopify revenue vs Facebook ad spend by campaign for last month." We handle sourcing the right data and stitching it together automatically, giving you live dashboards and instant answers without all the tedious setup.
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