DAX : why a single DAX with VAR does not work with FILTER

[TAUF]

Hello people, I'ld like to improve my DAX level by using more variables within a formula. 

I'm working with Contoso 2 dataset.

I want to calculate a sales amount with filter applied : with 2 DAX, I get the correct answer (357,73M).

• Sales Amount =

          SUMX(

              'Online Sales',

              'Online Sales'[Sales Quantity] * 'Online Sales'[Unit Price] - 'Online Sales'[Discount Amount]

          )

• Calculate 1 =

      CALCULATE(

          [Sales Amount],

          FILTER(

              'Online Sales',

              'Online Sales'[Unit Price] > 100 &&

              'Online Sales'[Discount Amount] > 10

              && RELATED(Products[Brand Name]) = "Contoso"

              )

      )

I wanted to use one DAX expression instead, however, the filter does not apply:

• xx_Calculate_1 =

  VAR total_sales = SUMX(

              'Online Sales',

              'Online Sales'[Sales Quantity] * 'Online Sales'[Unit Price] - 'Online Sales'[Discount Amount]

          )

  RETURN

  CALCULATE(

      total_sales,

      FILTER(

          'Online Sales',

          'Online Sales'[Unit Price] > 100 &&

          'Online Sales'[Discount Amount] > 10 &&

          RELATED(Products[Brand Name]) = "Contoso"

          )

  )

 Why my xx_Calculate_1 does not apply the filters ? 

 I try to understand and change the formula but the result is always the same...

Do you have any suggestions to help me understand and to create a DAX expression ? 

Thank you.

[TAUF]

Thank you so much for your reply and appreciate the reminder : variables are not measures !

[sjoerdvn · Accepted solution]

Variables are not measures!
Your variable is a scalar value, so applying a filter does exactly nothing. If you want to combine the two, try:

CALCULATE(SUMX('Online Sales',
            'Online Sales'[Sales Quantity] * 'Online Sales'[Unit Price] - 'Online Sales'[Discount Amount])
        ,'Online Sales'[Unit Price] > 100 
        ,'Online Sales'[Discount Amount] > 10
        ,Products[Brand Name] = "Contoso"
)