What Do You Use to Combine Queries in Power BI?

When you need to bring data from multiple tables together in Power BI, the tool you'll use is the Power Query Editor. This article will show you how to use its two primary features for combining data - Append and Merge - and explain exactly when to use each one.

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The Heart of Data Combination: Power Query Editor

Before jumping into the specifics, it's important to know where this all happens. All data combining in Power BI is done within the Power Query Editor. You can get there from the main Power BI Desktop screen by clicking the "Transform data" button on the Home ribbon.

Inside Power Query, your data sets are called "queries." A query is just a set of instructions for connecting to a data source (like an Excel file or a database) and shaping it. Combining queries means you're creating a new set of instructions to bring different datasets together into a single, unified view.

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Append vs. Merge: What’s the Difference?

Power Query gives you two main options for combining queries: Append and Merge. Understanding the difference is crucial because they solve very different problems.

• Append Queries: Think of this as stacking tables on top of each other. If you have data split into multiple tables with the exact same columns (like monthly sales reports), you append them to create one master table. The number of rows increases, but the number of columns stays the same.
• Merge Queries: Think of this as joining tables side-by-side. If you have two tables that share a common column (like a Sales table with a ProductID and a Products table with ProductID and ProductName), you merge them to enrich your data. The number of columns increases, while the number of rows typically stays the same.

Here’s a simple analogy:

• If you're stacking boxes of the same size, you're appending.
• If you're looking up a customer's address from one list and adding it to their order in another list, you're merging.

How to Append Queries: Stacking Data for a Full View

Use Append when your data is structured identically but spread across multiple tables or files. A classic example is having sales data for each month in a separate spreadsheet tab (e.g., "January_Sales", "February_Sales", "March_Sales"). To analyze the first quarter, you need to combine them into one table.

Step-by-Step Guide to Appending Queries

Let's assume you have tables for Q1, Q2, Q3, and Q4 sales results and you want to create a single table for the full year.

1. Open Power Query Editor: In Power BI Desktop, navigate to the Home ribbon and click "Transform data."
2. Locate Append Queries: In the Power Query Editor, stay on the Home ribbon. In the "Combine" group, you'll see the "Append Queries" button.
3. Choose "Append Queries as New": You have two choices:
4. Select Your Tables: An "Append" dialog box will appear.
5. Confirm and Review: Click "OK." Power Query will generate a new query, likely named "Append1." You'll see that it contains all the rows from your four quarterly tables, stacked vertically. You should rename this new query to something meaningful, like "Total_Annual_Sales."

Heads Up! For a clean append, your column headers must match perfectly across all tables. "Product ID" in one table and "ProductID" in another will result in two separate columns in your final table. Make sure the names and data types are consistent before you append.

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How to Merge Queries: Enriching Your Data With More Columns

Use Merge when you need to add details to one table from another. Imagine you have a table of Sales transactions that includes ProductID but not the product's name or category. A separate Products lookup table contains the ProductID along with the ProductName and Category. Merging lets you add the product name and category to your sales data.

Step-by-Step Guide to Merging Queries

Following our example, let's merge our Sales table with our Products table.

1. Get to Merge Queries: In the Power Query Editor, go to the Home ribbon and find "Merge Queries" in the "Combine" group. Just like Append, select "Merge Queries as New" to create a separate, combined table.
2. Configure the Merge Operation: The "Merge" dialog box is where you define the join.
3. Choose the "Join Kind": This tells Power Query exactly how to handle matching and non-matching rows.

For our scenario, "Left Outer" is perfect. We want to keep all our sales records and just attach product info. Click "OK."

1. Expand the New Column: A new query is created, but it looks a bit strange. It has all the columns from your Sales table plus a new column named Products that contains the word "Table" in every cell. This is correct! You need to expand this column to reveal the data. Click the two-arrow expand icon in the column header.
2. Select Columns to Add: A drop-down menu appears, listing all the columns from your Products table. Uncheck any you don't need (like ProductID, since you already have it). Select ProductName and Category. It's also good practice to uncheck "Use original column name as prefix" to avoid clunky column names like Products.ProductName.
3. Finish and Check: Click "OK." Your Sales table is now enriched with the product name and category, ready for deeper analysis in your Power BI reports.

Quick Tips for Combining Queries Painlessly

Keep these best practices in mind to avoid common frustrations:

• Check Data Types: Merging '123' (formatted as Text) with 123 (formatted as a Number) will not work. A quick check of data types on your key columns can save a lot of headaches.
• Keep Your Originals Clean: Always use "Append Queries as New" and "Merge Queries as New." This non-destructive approach preserves your original data transformations, making your process easier to debug and understand later.
• Mind the Cardinality: Mismatched or duplicated keys can cause unexpected results. If your lookup table has duplicate ProductIDs, a merge could create more rows than you started with.
• Watch for Mismatched Column Names: When appending, inconsistent column naming is the number one cause of errors. "Date" vs. "Sale_Date" will create two columns when you only wanted one.

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Final Thoughts

Combining data is a foundational skill in Power BI, and mastering the difference between Append and Merge is essential. An easy way to remember is: append adds rows for "more of the same," while merge adds columns for "more information about what you have." Using the Power Query Editor, you can transform scattered data into a clean, unified model ready for visualization.

While Power BI is a great tool, all this data wrangling can still be time-consuming, especially when joining data from multiple marketing or sales platforms. We created Graphed to remove this friction entirely. Instead of manually setting up Appends and Merges in Power Query, you can connect platforms like Google Analytics, Shopify, and Salesforce in seconds. Just ask a question in plain English like, "show me Shopify revenue by Google Ads campaign," and Graphed instantly handles the data blending and builds a live dashboard for you.