Beginning DAX with Power BI_ The SQL Pro’s Guide to Better Business Intelligence ( PDFDrive )

Chapter 2
Variables
You can use this technique with other DAX functions to create dynamic text-based
measures that may change depending on the current filter context. Consider the
following calculated measure:
Sales Text =
VAR SalesQty = SUM('Fact Sale'[Quantity])
VAR Text1 = "This month we sold "
VAR Text2 = " Items"
VAR Result = IF(
SalesQty > 0,
-- THEN --
Text1 & SalesQty & Text2,
-- ELSE --
"No sales this month"
)
RETURN Result
Here you assign the DAX SUM expression to the SalesQty variable. This is used later
in the IF function to test for the existence of sales to determine the output message. Note
the use of comments in the IF function to help clarify which code is being used to update
the Result variable.
This also shows how you can use variables to improve performance. The SalesQty
variable is potentially used twice in the IF function. If this formula was written without
using variables, the IF function would make two calls to the underlying column and
therefore take longer to arrive at the same result.
A similar function using text-based variables is one that generates a greeting
calculated measure. Creating a calculated measure using the code in Listing 2-1 tests
the current time of day and stores the hour of the day in the CurrentHour variable.
This is then used in a SWITCH function to generate appropriate text to be stored in the
GreetingText variable. This is then combined with other text to produce a measure that
you can use as a dynamic greeting on your report.
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