Do unused variables in measures cause performance issues?

[jordancole0517]

Hello! 

Just a general question...I'm wonder if unused variables not used after the "RETURN" might cause DAX to evaulate slower?

Thanks!

[Sergii24]

Hi @jordancole0517 and @DataInsights, apparently it seems they they do afect the perfomance (i.e. if you have 4 varialbes to define 4 different results of SWITCH() function, all of them will be evaluated, nevertheless only one will be true in a specific filter context).

Here what Alberto Ferrari says about it: "As a rule, think about a variable as always being evaluated, regardless of its use in the calculation."

Here is a great article of SQLBI on this topic - When are variables evaluated in DAX?

[jordancole0517]

Thanks, @DataInsights !

[DataInsights · Accepted solution]

@jordancole0517,

My understanding is that unused variables don't impair performance due to "lazy evaluation", meaning that a variable isn't evaluated until its first use. See the article below, as well as the comments at the end of the article for a detailed discussion:

https://www.sqlbi.com/articles/understanding-eager-vs-strict-evaluation-in-dax/