How to Union in Power BI

Trying to combine data from multiple tables in Power BI can feel confusing, especially when you have data spread across different files or sheets. If you need to stack identically structured tables - like monthly sales reports or campaign results from different ad platforms - Power Query's "Append Queries" feature is the tool you need. This article will walk you through exactly what an append operation is and how to use it step-by-step.

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What Exactly is a Union (or Append) in Power BI?

In the world of data, a "Union" is an operation that combines two or more tables by stacking them on top of one another. Power BI calls this function Append Queries.

Think of it like this: you have a stack of identically formatted spreadsheets, each one representing a month's sales data. An append operation takes these individual sheets and combines them into one tall, master spreadsheet with a complete list of all sales from all months.

For an append operation to work correctly, the tables you're combining should have the same columns in the same order and with the same column names. If they don't, Power BI will still do its best, but you might end up with unexpected null values where the data doesn't align.

Append vs. Merge: What's the Difference?

This is a common point of confusion. The easiest way to remember the difference is:

• Append (Union): Stacks rows on top of each other, making the table longer. It increases the number of rows. You use this when the data in the tables represents the same kind of information (e.g., sales data from different months).
• Merge (Join): Combines tables side-by-side based on a matching column, making the table wider. It increases the number of columns. You use this to enrich one table with data from another (e.g., adding product details from a Product table to your Sales table by matching on a ProductID).

In this guide, we are focused entirely on appending - making your tables longer.

Why Would You Need to Append Queries?

You’ll find yourself needing to append data in lots of common business scenarios. It’s the go-to solution whenever your data is segmented into separate files or tables on a regular basis.

Here are a few relatable examples:

• Combining Monthly or Quarterly Reports: You download sales or marketing performance reports as separate CSV files every month (e.g., Jan_Sales.csv, Feb_Sales.csv, Mar_Sales.csv). Appending lets you combine them into a single table for year-to-date analysis.
• Consolidating Regional Data: Your business operates in different regions, and you receive sales data in separate files like NorthAmerica_Sales.xlsx, Europe_Sales.xlsx, and Asia_Sales.xlsx. An append brings all regional sales into one unified view.
• Aggregating Data from Identical Systems: Imagine you’re managing two different Shopify stores. You can export the order data from each, and as long as you make the columns match, you can append them to analyze performance across both stores.
• Unifying Ad Campaign Data: While data structures differ broadly, you might standardize your exports from Google Ads, Facebook Ads, and LinkedIn Ads to have similar core columns like Campaign, Spend, Impressions, and Clicks. Appending allows you to create a high-level Total Ad Spend report.

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Getting Your Data Ready: The Golden Rule of Appending

Before you even click the "Append Queries" button, you need to ensure your data is ready. The single most important rule for appending is that your tables must have identical column structures.

This means:

• The column names must be exactly the same. Date is not the same as date (Power Query is case-sensitive). Sale_Amount is not the same as Sale Amount.
• The data type of each column should be consistent across tables. A Date column shouldn't be a text field in one table and a date/time type in another.

Example of Mismatched Columns:

Table 1: January_Sales

Table 2: February_Sales

If you try to append these tables, Power Query will get confused. It will create separate columns for Sale Date and Date, and for AOV and Average Order Value. Your final table will be a mess, filled with null values.

How to fix it:

Inside the Power Query Editor, before you append, rename the columns in one of the tables so they match the other perfectly. Double-click a column header to rename it.

Spending a minute to standardize your column names will save you a massive headache later.

Step-by-Step Guide: How to Append Queries in Power BI

With your data loaded into Power BI and your columns standardized, you're ready to perform the append operation. All the magic happens inside the Power Query Editor.

Step 1: Open the Power Query Editor

From the main Power BI Desktop screen, click on the Transform data button in the Home ribbon. This will launch the Power Query Editor, where you can see all of your connected data tables listed in the Queries pane on the left.

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Step 2: Choose 'Append Queries'

Select one of the tables you wish to combine. It doesn't matter which one you start with. In the Home ribbon of the Power Query Editor, find the Combine section and click the Append Queries button.

You will see two options:

• Append Queries: This performs an "inline" append, meaning it adds the rows from the second table directly into the table you currently have selected. The original table is modified.
• Append Queries as New: This combines the selected tables and creates a completely new, separate table. Your original tables are left unchanged.

Pro Tip: It is almost always better to choose Append Queries as New. This preserves your original data sources, making it easier to troubleshoot issues later. You can clearly see your raw data (Jan_Sales, Feb_Sales) and your combined data (All_Sales) separately.

Let's proceed with Append Queries as New.

Step 3: Combine Your Tables in the Append Window

After clicking "Append Queries as New," a dialog box will pop up. From here, you’ll choose which tables to combine. The view changes slightly depending on whether you are combining two tables or more than two.

Appending Two Tables:

If you're only combining two tables, the default dialog box is straightforward.

1. Your Primary table is pre-selected.
2. Click the dropdown under Table to append to the primary table and select your second table.
3. Click OK.

Power Query will instantly create a new query (e.g., Append1) that contains all the rows from both tables.

Appending Three or More Tables:

If you need to stack several tables, select the Three or more tables radio button.

1. The tables available for appending will be listed in the box on the left.
2. Select a table and click the Add > button to move it to the Tables to append box on the right.
3. Continue adding all the tables you want to stack.
4. Click OK.

Again, a new query will be created with all the data stacked together.

Step 4: Rename and Review Your New Table

Your newly created query will likely have a generic name like Append1. Right-click on it in the Queries pane and select Rename. Give it a descriptive name, like ConsolidatedSales or All_Campaign_Data.

Take a moment to scroll through the combined table. Check a few things:

• Does the total row count look right? (e.g., If Table 1 had 100 rows and Table 2 had 150, the appended table should have 250 rows).
• Are all columns filled with data? Or are there unexpected null values? If you see many nulls, it indicates a mismatched column name in your source queries that you need to fix.

Step 5: Close & Apply

Once you are happy with the combined table, click the Close & Apply button in the top-left corner of the Power Query Editor. This will save your changes and load the newly appended table into your Power BI data model, ready for creating visuals and reports.

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A Power Move: Appending Files from a Folder

If you regularly receive identically structured files (like dozens of monthly CSV exports), appending them one by one is tedious. A more efficient way is to use Power BI's Combine Files from Folder feature.

Instead of connecting to an individual file, you connect to the entire folder where they are stored (Data > Get Data > More... > Folder). Power BI will recognize all the files, and its Combine feature will automatically perform the append operation for you. Even better, whenever you drop a new file into that folder in the future, all you have to do is hit "Refresh" in Power BI, and the new data will be automatically appended to your dataset.

Final Thoughts

Appending queries in Power BI is a fundamental technique for combining and consolidating datasets. By stacking tables with similar structures, you can create a single, unified source of truth for your reporting, whether you're analyzing sales across different time periods, regions, or platforms. The key is to ensure your columns match before you start.

While mastering tools like Power BI is incredibly valuable, we know that the initial steps of connecting data sources and manually cleaning, stacking, and preparing tables consume hours every week. Instead of wrestling with column names and transformations, you can simplify the entire process using our platform. We designed Graphed to connect directly to platforms like Shopify, Google Analytics, and Facebook Ads, automatically bringing all your data into one place. From there, you just ask questions in plain English - like "Show me total sales by month for the last year" - and the dashboards and charts build themselves, no manual appending required.