Often, you will want to filter data in Tableau in order to perform an analysis on a subset of data, narrow your focus, or drill into detail. Tableau offers multiple ways to filter data.

If you want to limit the scope of your analysis to a subset of data, you can filter the data at the source using one of the following techniques:

• Data Source Filters are applied before all other filters and are useful when you want to limit your analysis to a subset of data. These filters are applied before any other filters.
• Extract Filters limit the data that is stored in an extract (.tde or .hyper). Data source filters are often converted into extract filters if they are present when you extract the data.
• Custom SQL Filters can be accomplished using a live connection with custom SQL, which has a Tableau parameter in the WHERE clause. We'll examine parameters in Chapter 4, Starting and Adventure with Calculations.

Additionally, you can apply filters to one or more views using one of the following techniques:

• Drag and drop fields from the data pane to the Filters shelf.
• Select one or more marks or headers in a view and then select Keep Only or Exclude, as shown here:

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• Right-click any field in the data pane or in the view, and select Show Filter. The filter will be shown as a control (examples include a drop-down list and checkbox) to allow the end user of the view or dashboard the ability to change the filter.
• Use an action filter. We'll look more at filters and action filters in the context of dashboards.

Each of these options adds one or more fields to the Filters shelf of a view. When you drop a field on the Filters shelf, you will be prompted with options to define the filter. The filter options will differ most noticeably based on whether the field is discrete or continuous. Whether a field is filtered as a dimension or as a measure will greatly impact how the filter is applied and the results.