DAX approach to finding which parent records have no related records

[careyd]

*If I am not supposed to post a question here, please let me know. Thanks!*

Thanks for reading and for helping if you can. I have not been able to come up with a solution for this. I am just learning DAX and appreciate any guidance. 

Table A has a one>many cardinality with Table B.

Some Table A records do not have related records in Table B.

When a Table A record DOES NOT have a foreign key in Table B, I want to use a value from a Table A column.

When a Table A record DOES have a foreign key in Table B, I want to sum the values in a Table B column.

Table A (Tasks)               Table B - Assignments          Table A Calculated Value in Power Pivot

Key: 1                             Foreign Key: 1                       Sum of Table B[Assign_hours] = 4.5     

Plan_Hours = 5              Assign_Hours = 2

                                      Foreign Key: 1

                                      Assign_Hours = 1.5   

Key: 2                             (no record)                             Table A Plan_Hours = 3

Plan_Hours = 3

Thank you!

[tamerj1]

Hi @careyd 

power pivot does not have a calculated table feature. Do you mean power query, power bi or pivot table?

[careyd]

Thanks for the reply @tamerj1! That may be the root of the problem, then. Though I do see a CALCULATETABLE function when working with DAX in Power Pivot. 

[tamerj1 · Accepted solution]

Yes most of the table functions are available in power pivot. You can use any function in your measures and calculated tables but the final result of your calculation must be a scalar value. if a table is returned you will receive an error.

[careyd]

Okay. I appreciate your insight. I'll investigate a different approach. Thank you!