# Tableau Prep Builder: Unions & Joins (Part 7 of 7)

> This is content from just-tim, the data-and-analytics channel by Tim Ngwena (formerly 'Tableau Tim'). Tim has 12+ years of hands-on BI experience and covers Tableau most of all, plus Power BI, Looker, Hex, SQL and data modelling, the analytics industry, and the craft of doing the job — always tool-agnostic and honest about the trade-offs.

- **Author:** Tim Ngwena (just-tim, https://just-tim.com/about)
- **Published:** 2020-01-27
- **Format:** Video · 19 min watch · transcript available
- **Topics:** Data prep
- **Tools:** Tableau (join, prep, union)
- **Canonical:** https://just-tim.com/posts/tableau-prep-builder-unions-joins-part-7-of-7
- **Watch:** https://www.youtu.be/f7tTlG2mfxc

This is the seventh and final video in my Tableau Prep for Excel users series, where I cover joins and unions in Tableau Prep Builder. I walk through how to stack data with unions, build join clauses and choose join types, spot duplicated records, and finally export your flow as a hyper or CSV file.

## Key takeaways

- Unions stack tables on top of each other, combining rows from data sets with similar column layouts, while joins add columns by matching records side by side via a join clause.
- Tableau Prep colour-codes columns by their source data, so you can visually trace which rows or fields come from which branch and check the proportions in the summary view.
- The union step flags mismatched fields when column names don't align, letting you manually pair columns to merge them.
- Choosing the wrong join type or omitting part of the join clause can explode your row count beyond the input total, an immediate alarm bell for accidental duplication.
- You can run a flow and output to a Tableau hyper file (fast and compressed) or CSV for Excel, and run it from the output button, the output step, or the top toolbar with caching speeding up reruns.

## Chapters

- 0:00 Recap and where joins and unions live
- 2:32 Building a simple union
- 6:44 Handling mismatched fields
- 7:52 Anatomy of a join
- 10:21 Join types and exploding row counts
- 15:25 Outputting a file from Tableau Prep
- 18:36 Series wrap-up

Watch the full video, read the transcript and use chapter deep-links on the page: https://just-tim.com/posts/tableau-prep-builder-unions-joins-part-7-of-7

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just-tim — Data and analytics, with a point of view. · https://www.youtube.com/channel/UC7HYxRWmaNlJux-X7rNLZyw · https://twitter.com/TableauTim · https://www.linkedin.com/in/timngwena