Summarizing data from 2 different tables with Date

Create a measure like

Combined Value = SUM( Historic[Value] ) + SUM( Future[Value] )

Put this in a matrix with columns from your date table.

Hello,johnt75 ,gmsamborn and uzuntasgokberk ,thanks for your concern about this issue.

Your answers are excellent!
And I would like to share some additional solutions below.

Hi,unknown917 .I am glad to help you.
I tried the idea you suggested for the DATE table that has all the data, and added a new calculated column that has all the data from both tables, which ensures that the data is displayed normally as one row in the matrix

My test data:

This is the optimized dax code

The model relationship:

This is my test code

AllDailySales = 
IF (
    SELECTCOLUMNS ( RELATEDTABLE ( historical ), "a", [DailySales] ) <> BLANK (),
    SELECTCOLUMNS ( RELATEDTABLE ( historical ), "a", [DailySales] ),
    SELECTCOLUMNS ( RELATEDTABLE ( future ), "b", 'future'[Forecast daily sales] )
)

Suggestion2

I also tested the solution proposed by johnt75, which uses a matrix to present the data, and can achieve similar results.

TestAllMeasure =
SUM ( 'historical'[DailySales] ) + SUM ( 'future'[Forecast daily sales] )

I hope my suggestions give you good ideas, if you have any more questions, please clarify in a follow-up reply.
Best Regards,
Carson Jian