Mastering Data Union in Tableau: Manual vs. Wildcard Explained

Overview

Data union in Tableau is a row‑level data combination method that merges two or more tables by appending their records into a single, longer dataset, provided the tables share a similar structure. In a union, Tableau vertically stacks the rows from each source table - such as multiple monthly files, regional extracts, or identically formatted worksheets - into one consolidated table, automatically aligning fields with matching names and creating separate fields for any mismatches. Because unions make data taller rather than wider, they are ideal for scenarios where information is split across multiple files with the same schema, enabling seamless aggregation, filtering, and analysis across the combined dataset within a single unified view.

Example of Data Union

Manual Union: Full Control, Hands-On Setup

Manual data union in Tableau is the hands‑on method of combining multiple tables by explicitly selecting and stacking them into a single, unified dataset. It gives you full control over which sheets, files, or tables are included, making it ideal when you’re working with a small number of sources or when their names aren’t consistent enough for automated pattern matching. By manually dragging tables into the union interface, you ensure that only the intended data is appended, allowing for precise, deliberate preparation of analysis‑ready datasets.

To manually union data;

Connect your data set and drag the first table to the canvas.

Open the drop-down menu and select Convert to Union...

Select Specific (Manual) tab and drag the specific tables to the canvas to union.

Click Ok and review your data.

Wildcard Union: Automated, Scalable, Pattern-Based

Wildcard data union in Tableau is the automated way of combining multiple tables by matching their names to a pattern, allowing Tableau to dynamically include every file or worksheet that fits that pattern. Instead of manually selecting each table, you define a naming rule - such as Sales_* or 2025_Q* - and Tableau automatically unions all matching sources, including new ones added later. This makes wildcard unions ideal for large, consistently named datasets and workflows that need scalability and ongoing updates.

To union data using wildcard;

Repeat the same process, but in this case select Wildcard (automatic).

Specify the string Tableau should match, for my case I want Tableau to match “Data Yr ” - so any data file that contains “Data Yr ” in my subfolder or parent folder will be added into the union.

Note: Any future files saved in the same location and meeting the same criteria will be included in the union automatically.

Click Ok and review your data.

Conclusion

Mastering data unions in Tableau is ultimately about choosing the right strategy for the structure and scale of your data and understanding how Manual and Wildcard unions complement different analytical workflows. Manual unions give you precise, hands-on control when working with a small number of inconsistently named tables, while wildcard unions unlock automation and scalability by dynamically capturing large collections of consistently named files. Together, they allow you to transform fragmented, multi-source datasets into unified, analysis-ready tables that support cleaner modelling, faster insights, and more reliable dashboards. By standardizing naming conventions, maintaining consistent schemas, and validating mismatched fields, you can ensure your unions remain robust and future-proof. Whether you’re consolidating monthly reports, merging regional extracts, or preparing log files for time-series analysis, understanding these union techniques empowers you to streamline your data preparation process and fully leverage Tableau’s analytical capabilities.

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