VALUE_DIFFERENCE

/*
Function: VALUE_DIFFERENCE
Purpose: This function calculates the difference between two values present in different tables that both have a relationship with another table.
Parameters: 
- @table1_value: The value from the first table.
- @table2_value: The value from the second table.
Return: The difference between @table1_value and @table2_value.
Exceptions: This function will not work if there's not a relationship between the four tables involved.
*/

VALUE_DIFFERENCE:=
CALCULATE (
    VAR Table1_Total = SUM ( Table1[@table1_value] )
    VAR Table2_Total = SUM ( Table2[@table2_value] )
RETURN
    Table1_Total - Table2_Total,
    RELATECOLUMN (
        'CommonTable',
        RELATED ( Table1[@table1_value] ),
        RELATED ( Table2[@table2_value] )
    )
)

This code will return the difference between the sums of the two designated columns (@table1_value and @table2_value) from Table1 and Table2 respectively. It assumes that there's a CommonTable in the data model that is in a relationship with both Table1 and Table2.

The RELATECOLUMN function is used to create a new column in the CommonTable containing the corresponding values from the designated columns in Table1 and Table2.

Code Usage Example:

Let's say you have three tables: Sales, Budget and Product. The Sales and Budget tables both have a 'ProductId' column, and record 'Revenue' and 'BudgetAmount' respectively. Both are in a relationship with the Product table via the 'ProductId'. The VALUE_DIFFERENCE could be used as follows:

Revenue_Budget_Difference:= VALUE_DIFFERENCE('Sales'[Revenue], 'Budget'[BudgetAmount])

This will return the difference between actual Revenue and BudgetAmount for each product. Please note that this code should be used directly in measures.