Lesson 3: Mark as Date Table
In Lesson 2: Add Data, you imported a dimension table named DimDate. While in your model this table is named DimDate, it can also be known as a Date table, in that it contains date and time data.
Whenever you use DAX time-intelligence functions in calculations, as you'll do when you create measures a little later, you must specify date table properties, which include a Date table and a unique identifier Date column in that table.
In this lesson, you'll mark the DimDate table as the Date table and the Date column (in the Date table) as the Date column (unique identifier).
Before we mark the date table and date column, we need to do a little housekeeping to make our model easier to understand. You'll notice in the DimDate table a column named FullDateAlternateKey. It contains one row for every day in each calendar year included in the table. We'll be using this column a lot in measure formulas and in reports. But, FullDateAlternateKey is not really a good identifier for this column. We'll rename it to Date, making it easier to identify and include in formulas. Whenever possible, it's a good idea to rename objects like tables and columns to make them easier to identify in client reporting applications like Power BI and Excel.
Estimated time to complete this lesson: 3 minutes
This topic is part of a tabular modeling tutorial, which should be completed in order. Before performing the tasks in this lesson, you should have completed the previous lesson: Lesson 2: Add data.
To rename the FullDateAlternateKey column
In the model designer, click the DimDate table.
Double click the header for the FullDateAlternateKey column, and then rename it to Date.
To set Mark as Date Table
Select the Date column, and then in the Properties window, under Data Type, make sure Date is selected.
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 the Date column as the unique identifier. It will usually be selected by default. Click OK.
Go to the next lesson: Lesson 4: Create Relationships.