If you are connected to a data source that has been modified, you can immediately update Tableau Desktop with the changes by selecting a data source on the Data menu and then selecting Refresh.

Not every connection will behave in the same way. There are three primary connection types: Live Connection, Extract, and Published Data Source. The type of connection is displayed by the icon next to your data source in the Data Pane.

Live Connection
A live connection sends queries to the database and updates the view depending on the results. However, the specific fields queried are defined when the connection is initially created. Refreshing the data source will update any new or changed fields.

Extract
Refreshing an extract will query the data source the extract was created from and rebuild the extract. This process might take some time, depending upon the size of the extract.

Published Data Source
When connected to a Published Data Source, the data source can be either a live connection or an extract. Selecting the Data Source tab will display whether the Published Data Source is a live connection or an extract. If the data source is an Extract, all refreshes of the extract are managed by Tableau Server and can only be refreshed by the server.