Discussion: To Variable or not Variable in IF statements, that is the question.

[StuartSmith]

It seems to be the common practice to declare all variables first and then use them in the measure, but too optimise measures should you declare variables even if you might not need them in an IF statement or avoid Variables and simply put the code from the variables in the IF statement?

So as an example, 

Variable_Measure = 

VAR Variable1 = Blah1, Blah, Blah, Blah

VAR Variable2 = Blah2, Blah, Blah, Blah

VAR Variable3 = Blah3, Blah, Blah, Blah

Return

IF(Variable1 = True, Variable2, Variable3)

The above Variables could be complex calculations, using lots of system resources even before the IF statement and then depending on the IF statement result, the variable might not be used, so unnecassary declaring a variable and useing system resources.

NonVariable_Measure =

IF(Blah1, Blah, Blah, Blah = True, Blah2, Blah,  Blah, Blah, Blah3, Blah, Blah, Blah)

In the above, no variables are pre-loaded/calculated and calculated only when needed depending on the IF statement result.  Surely this is a more efficient way than using variables?

I hope that makes sense.

[Alex87 · Accepted solution]

It is important to know why using variables in DAX is so common. You shouldn't just create variables for the sake of it. Instead, use them to break down complex problems into simpler chunks, make your formulas easier to manage, and make sure each part is only calculated once. But, keep an eye on performance too. It’s a good idea to play around with different approaches and test their performance in DAX Studio to see what works best.

[StuartSmith]

Thanks for the input and sort of confirmed the approach I am taking.

[v-zhengdxu-msft · Accepted solution]

Hi @StuartSmith 

This is a dialectical question.

Just as @Alex87 said, the using of variables is important.

Variables can enhance performance by avoiding redundant calculations. When you declare a variable, its value is computed once and reused throughout the measure. This can significantly reduce query time, especially for complex expressions.

For example, if the outcome is 
IF(Variable1 = Variable2, Variable2, Variable3)

The Variable1,2,3 only calculate once.

But this formula will calculate Blah2, Blah,  Blah twice.
IF(Blah1, Blah, Blah, Blah = Blah2, Blah,  Blah, Blah, Blah2, Blah,  Blah, Blah, Blah3, Blah, Blah, Blah)

If the expression is more complex, there will be more redundant calculations。

Well-named variables make your DAX formulas more readable. They act as placeholders for intermediate results, making the measure easier to understand.

Variables allow you to isolate specific parts of your formula for testing. You can temporarily modify the RETURN expression to output the variable value during debugging.

While variables offer benefits, there are scenarios where avoiding them might be more efficient, for straightforward calculations, directly using expressions within the measure can be more concise.

Best Regards

Zhengdong Xu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[Alex87 · Accepted solution]

It is important to know why using variables in DAX is so common. You shouldn't just create variables for the sake of it. Instead, use them to break down complex problems into simpler chunks, make your formulas easier to manage, and make sure each part is only calculated once. But, keep an eye on performance too. It’s a good idea to play around with different approaches and test their performance in DAX Studio to see what works best.