DAX Days Between Invoices Calculation

DAX Formula with Error Analysis

Provided DAX Formula Draft

The initial DAX formula provided is as follows:

DaysBetweenInvoices = 
VAR CurrentInvoiceDate = MAX(dimCalendar[Date])
VAR PreviousInvoiceDate = 
    CALCULATE(
        MAX(dimCalendar[Date]),
        FILTER(
            fact_Table,
            fact_Table[Invoice No ] = 

Issues Identified

1. Incomplete Formula: The formula is incomplete and does not specify how to filter or compute the PreviousInvoiceDate. The filter context is missing a condition or value for comparison.
2. Potential for Errors: Without a complete logical structure, if executed, it will lead to an error message, specifically indicating an issue with the incomplete syntax in the formula.

Complete Example Formula

To provide a complete understanding, let us create a full version of the formula that is intended to calculate the difference in days between the current and previous invoices, followed by an explanation:

DaysBetweenInvoices = 
VAR CurrentInvoiceDate = MAX(dimCalendar[Date])
VAR PreviousInvoiceDate = 
    CALCULATE(
        MAX(dimCalendar[Date]),
        FILTER(
            fact_Table,
            fact_Table[Invoice No] < MAX(fact_Table[Invoice No]) 
        )
    )
RETURN
    DATEDIFF(PreviousInvoiceDate, CurrentInvoiceDate, DAY)

Explanation of the Formula

1. Variables Definition:

   • CurrentInvoiceDate: This variable captures the maximum date value from the dimCalendar table, representing the latest invoice date in the current filter context.
   • PreviousInvoiceDate: This variable calculates the maximum date of the previous invoice by filtering fact_Table. The filter specifies that it should find the invoice number which is less than the maximum invoice number in the current context.

2. Return Value:

   • The function DATEDIFF is used to compute the difference in days between PreviousInvoiceDate and CurrentInvoiceDate. The unit of measurement is specified as DAY.

Practical Illustration

Assuming the following scenario in a dataset:

• dimCalendar contains dates from January 1, 2022, to December 31, 2022.
• fact_Table contains invoice numbers and related attributes.
• If the latest invoice (Invoice No 102) was issued on August 15, 2022, and the previous one (Invoice No 101) was issued on August 6, 2022, the calculation would result in a difference of 9 days.

Conclusion

When using the incomplete version of the formula, execution would lead to an error due to syntax issues. The solution provides a valid and fully functional DAX formula for calculating the number of days between the current and previous invoices within the data model.

For further learning on DAX and effective data modeling practices, consider exploring resources available on the Enterprise DNA Platform.