Specify Mark as Date Table for use with Time Intelligence (SSAS Tabular)
In order to use time intelligence functions in DAX formulas, you must specify a date table and a unique identifier (datetime) column of the Date data type. Once a column in the date table is specified as a unique identifier, you can create relationships between columns in the date table and any fact tables.
When using time intelligence functions, the following rules apply:
When using DAX time intelligence functions, never specify a datetime column from a fact table. Always create a separate date table in your model with at least one datetime column of Date data type and with unique values.
Make sure your date table has a continuous date range.
The datetime column in the date table should be at day granularity (without fractions of a day).
You must specify a date table and a unique identifier column by using the Mark the Date Table dialog box.
Create relationships between fact tables and columns of Date data type in the date table.
To specify a date table and unique identifier
In the model designer, click the date table.
Click the Table menu, then click Date, and then click Mark as Date Table
In the Mark as Date Table dialog box, in the Date listbox, select a column to be used as a unique identifier. This column must contain unique values and should be of Date data type. For example:
7/1/2010 12:00:00 AM
7/2/2010 12:00:00 AM
7/3/2010 12:00:00 AM
7/4/2010 12:00:00 AM
7/5/2010 12:00:00 AM
If necessary, create any relationships between fact tables and the date table.