title: How to subtract columns from two different tables in Power BI
body: <p>I am new to DAX funciton on Power BI. I have two tables as Parent table Dim_TargetSpec and Child table Fact_Yield. These tables have relationship via Spec column. I want to substract by Dim_TargetSpec[Target_Fat] - Fact_Yield[Average Fat] and this is the DAX function</p>
  <pre><code>Fat_Diff = Dim_TargetSpec[Target_Fat] - LOOKUPVALUE(Fact_YieldReport[Average Fat],Fact_YieldReport[Spec], Dim_TargetSpec[Spec],0)
  </code></pre>
  <p>This function returns unexpected results exactly the Dim_TargetSpec[Target_Fat] column:</p>
  <pre><code>    Spec    Target_Fat  Average_Fat   Fat_Diff
      AFC_2   15.2        14.2          15.2
      AFC_2   15.5        16.00         15.5
  </code></pre>
  <p>My expected correct results are:</p>
  <pre><code>Spec    Target_Fat  Average_Fat   Fat_Diff
  AFC_2   15.2        14.2           1.0
  AFC_2   15.5        16.0          -0.5
  </code></pre>
  <p>Could anyone please help me to correct the DAX function so getting correct results?</p>
  <p>Much appreciated for your help
  Thanks</p>