Creating a New Column in a Date Table with DAX

Objective

To create a new column named Past Dates in the Dates table that contains past dates relative to today's date.

Key Concepts

• DAX: The Data Analysis Expressions language used in Power BI, Power Pivot, and SSAS Tabular models for data manipulation and calculations.
• Date Table: A table that contains a list of dates used for time-based analysis.

Steps

1. Open Power BI Desktop.
2. Navigate to the Data view.
3. Select the Dates table where you want to add the new column.
4. Create a New Column using a DAX expression.

DAX Code

The following DAX expression will create the Past Dates column:

Past Dates = 
IF(Dates[Date] < TODAY(), Dates[Date], BLANK())

Explanation

• IF function: Evaluates a condition.
  • Dates[Date] < TODAY(): Checks if the date in the Dates table is less than today's date.
  • If the condition is true, it returns Dates[Date], meaning it includes the date.
  • If false, it returns BLANK(), ensuring that future dates do not appear in the Past Dates column.

Best Practices

• Date Table: Ensure that your Dates table is marked as a date table in Power BI for optimal performance.
• Avoid Overloading: Only include necessary columns in your analysis to maintain clarity within your data model.

Additional Resources

For deeper insights and advanced usage of DAX, consider exploring courses on the Enterprise DNA Platform. These can enhance your skills in data modeling and DAX calculations.

Conclusion

The DAX code provided effectively creates a new column for past dates in the Dates table. Implementing this snippet will allow for better time-based analysis within your reports.