Database servers, such as SQL Server, MySQL, Vertica, and Oracle, host data on one or more server machines and use powerful database engines to store, aggregate, sort, and serve data based on queries from client applications. Tableau can leverage the capabilities of these servers to retrieve data for visualization and analysis. Alternately, data can be extracted from these sources and stored in an extract (.hyper or .tde).

As an example of connecting to a server data source, we'll demonstrate connecting to SQL Server. If you have access to a server-based data source, you may wish to create a new data source and explore the details. However, there is no specific example to follow in the workbook in this chapter. As soon as the Microsoft SQL Server connection is selected, the interface displays options for some initial configuration as follows:

A connection to SQL Server requires the Server name, as well as authentication information.

A database administrator can configure SQL Server to use Windows Authentication or a SQL Server username and password. With SQL Server, you can also optionally allow for reading uncommitted data. This can potentially improve performance, but may also lead to unpredictable results if data is being inserted, updated, or deleted at the same time Tableau is querying. Additionally, you may specify SQL to be run at connect time using the Initial SQL... link in the lower-left corner.

Once you click the orange Sign In button, you will see a screen that is very similar to the connection screen you saw for Excel. The main difference is on the left, where you have an option for selecting a database, as shown in the following screenshot:

Once you've selected a database, you will see the following:

• Table: This shows any data tables or views contained in the selected database.
• New Custom SQL: You may write your own custom SQL scripts and add them as tables. You may join these as you would any other table or view.
• New Union: You may union together tables in the database. Tableau will match fields based on name and data type, and you may additionally merge fields as needed.
• Stored Procedures: You may use a stored procedure that returns a table of data. You will be given the option of setting values for stored procedure parameters, or using or creating a Tableau parameter to pass values.

Once you have finished configuring the connection, click a tab for any sheet to begin visualizing the data.