title: PowerBi DAX equivalent for SUMIFS with current row value as filter
body: <p>In Excel I could, if I was in a table called 'Sales' that had four columns</p>
  
  <p><strong>Sales</strong></p>
  
  <pre><code>Month, CustomerId, ProductId, TotalQuantity
  Jan,1, CAR,
  Feb,1, CAR,
  </code></pre>
  
  <p>I could add a formula:</p>
  
  <pre><code>=SUMIFS(Sales[Quantity],Sales[CustomerId],[@[CustomerId]])
  </code></pre>
  
  <p>That would go to the Sales table and sum the CustomerID column filtered by the CustomerID of the current row where the formula has been entered.</p>
  
  <p>I am attempted to replicate this in a PowerBI Calculated Row but I can't get the @ working for a row reference. It comes across like</p>
  
  <pre><code>TotalQuantity = CALCULATE(SUM(Sales[Quantity]),Sales[CustomerId] = Sales[CustomerId]))
  </code></pre>
  
  <p>Any idea how to get the equivalent <code>@</code> working?</p>