In Chapter 1, Catching Up with Tableau 2018, about data connection, you saw how to create joins between different Tables of the same dataset. With cross-database Joins, you can create joins between different tables from different connections of different types. It's a great way to add new dimensions to your analysis.

As an example, let's create a join between Sample-Superstore and another Excel File, Reimbursement, containing the reimbursed orders.

Here's what the Reimbursement table contains:

Here's how to create a cross-database Join between those two files:

1. Open Tableau, and click on the saved Data Source, Sample - Superstore.
2. Click on Data Source at the bottom-left of the window to open the Data Source workplace.

3. Next to Connections, click on Add to connect to another File or Server, as highlighted in the following screenshot:

4. Search and select the Reimbursement Excel File. Tableau automatically opens it in the same Data Source page, underneath Sample - Superstore.
5. Add the Reimbursement table as a usual left Join:

6. Create, in a new Worksheet, a visualization that combines the sales and the reason for reimbursement using a single data source:

A cross-database Join has the same disadvantage as a standard join: it can duplicate the data. However, it's a great feature that allows you to combine multiple datasets of different types in a unique Data Source.

The next section presents another way of combining two datasets.