DAX VAR defining named variables in the middle of the measure code

问题

I have been presented here with a bizarre exploitation of VAR function. So far I have encountered VAR in the beginning of the measure, right after the equal sign. See the code below:

Expected Result =
SUMX (
    VALUES ( Unique_Manager[Manager] ),
    VAR SumBrand = CALCULATE ( SUM ( Budget_Brand[BudgetBrand] ) )
    VAR SumProduct = CALCULATE ( SUM ( Budget_Product[BudgetProduct] ) )
    RETURN
        IF ( ISBLANK ( SumProduct ), SumBrand, SumProduct )
)

Here VAR is nested deeply inside the measure code. Needless to say that this is a fantastic feature of VAR. I have been trying to use that feature in my measures with no luck. For example, this works:

Measure_good = CALCULATE( 
    SUM(table[Amount])
)

While this does not work:

Measure_bad = CALCULATE( 
    VAR inside_measure = SUM(table[Amount])
)

What are the rules for using VAR in this unusual way?

回答1:

A VAR statement needs a matching RETURN. You can declare several variables after one another, but then you must use a RETURN command to pass the variables back to the main calculation, where the variable can then be used for evaluation in an IF statement or whatever

I have not tested this, but your Measure_bad should be like this (although it doesn't make much sense to use a VAR if all the remainder of the formula returns the variable)

Measure_bad = CALCULATE( 
    VAR inside_measure = SUM(table[Amount])
    RETURN
    inside_measure
)

回答2:

When you use a variable, via a VAR statement, you must always include a RETURN statement to essentially tell DAX you are going to consume those variables and return a value. In your last example, you do not include a RETURN statement and, therefore, you will get an error. In your first example, you have a RETURN statement, thus, no error. In your second example, you are not using variables.

回答3:

I have found a relevant information in documentation:

https://docs.microsoft.com/en-us/dax/var-dax#remarks

An expression passed as an argument to VAR can contain another VAR declaration.

When referencing a variable:

Measures cannot refer to variables defined outside the measure expression, but can refer to functional scope variables defined within the expression.

Variables can refer to measures.

Variables can refer to previously defined variables.

Columns in table variables cannot be referenced via TableName[ColumnName] syntax.

来源：https://stackoverflow.com/questions/57769750/dax-var-defining-named-variables-in-the-middle-of-the-measure-code

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