Enough for the theory, let's create a simple Join between the Orders and People tables from Sample - Superstore. Before we start, let's see what those tables contain:

• Orders is the main table (the left one). We already used it in Chapter 3, A First Dashboard and Exploration, and it contains the profit.
• People is a table that contains only four lines and two columns. It associates a region with a person.

Our goal is to create a Data Source that allows us to look at the profit ( which exists only in the Orders table) by person (which exists only in the People table).

Open Tableau and follow these instructions:

1. Connect to the Sample-Superstore Excel file in your Tableau repository (use the Connecting to data section from Chapter 3, A First Dashboard and Exploration, if you don't remember the file's location).
2. In the Data Source workspace, drag and drop the Orders table.

3. Drag and drop the People table next to Orders, as in the following screenshot:

4. Tableau automatically creates a Join between the two tables with Region as the link, as shown in the following screenshot:

5. On the preview, you can see, on the right, the two new columns from the Person table:

6. The Data Source is ready. You can test it on a Worksheet and display the profit by person as we wanted.

This is a first and simple example. You can build more complex Joins by adding more tables. In the following screenshot, we also added the Returns table:

Be careful when multiplying the Joins; it has an impact on performance. 

After Joins, the next interesting feature is Unions.