How you work with dates in Tableau depends on whether you are using a relational or cube (multidimensional)data source. This section discusses the differences.
Dates in Cube (Multidimensional) DataSources
In Tableau Desktop, cube (multidimensional) data sources are supported only in Windows.
For cube data sources, datesdimensions are usually organized into hierarchies that contain levelssuch as year, quarter, and month. In addition, some multidimensionaldata sources have time intelligence enabled, which makes it possible to look at data levels differentways, such as Months by Year, Monthsby Quarter, Weekends, etc. These levels are represented as attributes ofthe hierarchy. Hierarchies and attributes are defined whenthe cube is created and you cannot modify them in Tableau. For example,the Year dimension from an Oracle Essbase data sourceis shown below.
When you place a multidimensional date ona shelf, the field is treated like any other dimension. For example,you can drill down, drill up, and so on.
Dates in Relational Data Sources
For relationaldata sources, dates and times are automatically placed in the Dimensions areaof the Data pane and are identified by the date 
or date-time 
icon. For example, the OrderDate and Ship Date dimensionsfrom an Excel data source are shown below.
When you place a relationaldate on a shelf, the field name is automatically modified to reflectthe default date level. Tableau defines the default date level tobe the level at which there are multiple instances. For example,if the date field includes multiple years, the default level isyear. However, if the date field contains data for just one yearbut includes multiple months, then the default level is month.
Ifyou don’t want Tableau to automatically select a date level andwould rather have a date dimension be a continuous field, you canright-click (control-click on Mac) the field in the Data pane and select Convert to Continuous.The dimension then turns green in the Data pane; now when you use that dimension in a view, it will be continuous. You can easily revert back by selectingConvert to Discrete from the field’s context menu in the Data pane.You can also convert a field in the view to continuous while it is ona shelf by selecting Continuous on its context menu (which you can see when you right-click (control-click on Mac) the field). The field onthe shelf turns green but the field in the Data pane is stilldiscrete.
