Mark as Date Table Dialog Box (SSAS)
The Mark as Date Table dialog box appears when you click the Table menu, then click Date, and then click in the Mark as Date Table. Date tables are used with time intelligence functions. In order to create a relationship with a data table, you must specify a column with unique values to be used as a unique identifier for the table.
The Date listbox lists all of the columns in the table. To select a column to be used as a unique identifier, you must select a column of the date data type and it must contain unique values.