Every Tableau workbook can contain multiple data connections, worksheets, views, and dashboards.
The basic unit is the data connection.

Each worksheet can have one view and multiple data connections. Worksheets can share the same data connections.
A dashboard can contain any number of views, regardless of which data connections are used by the view.
If you modify a data connection, any worksheet or view that uses this data connection changes to reflect the modification.
Create a new data connection when you need to change the data without affecting the current worksheets. You can connect to a new data source, connect to a new table in the same data source, add tables, remove tables, change the fields used, or re-write custom SQL.
There are two methods to create an additional data connection. The first is to add a new data connection. The second is to duplicate and modify an existing data connection.