Comparing dates from 2 tables to select a value for the exchange rate

[DannyMiletic]

Hi Power BI Community - can anyone help me with the measure that I need to write to accomplish this? I am really striking out on this and need help. I have 2 tables; Table A - exchange rate table with rates posted at the end of each month, and table B - invoice table with dates, amounts in local currency and currency type. I need a measure that will compare the invoice_date and currency_ID to the exchange rate table and bring back the correct rate. The exchange rates are posted at the end of the month so that the 7/31/2020 exchange rate is applied to invoices during the month of July.

[MarkLaf · Accepted solution]

Assuming VALID_UNTIL and CURRENCYFROM_ID are a composite key for Table A, you could add a calculated column to both tables and relate them that way to then pull over corresponding exchange rate. Calculated column DAX would look like:

'Table A'[ExId] = 
VAR _dt = 'Table A'[VALID_UNTIL] 
VAR _exId = 'Table A'[CURRENCYFROM_ID]
RETURN
_exId  * 10^8 
+ YEAR( _dt  ) * 10^4 
+ MONTH( _dt ) * 10^2 
+ DAY( _dt )

'Table B'[ExId] = 
VAR _dt = EOMONTH( 'Table B'[invoice_date], 0 )
VAR _exId = 'Table B'[Currency_ID]
RETURN
_exId  * 10^8 
+ YEAR( _dt  ) * 10^4 
+ MONTH( _dt ) * 10^2 
+ DAY( _dt )

[DannyMiletic]

Thank you - this was very helpful!

[DannyMiletic]

Thanks - I will try it.