title: Query only data during current month
body: <p>I have a simple SQL query as below:</p>
  
  <pre><code>select   ProjectNo,
           CostCat,
           SummaryCostCat,
           CreditorEmployeeName,
           UnitCost,
           TotalCost,
           TransactionDate
  from dbo.NGPCostPosition
  </code></pre>
  
  <p>This gives me a selection of data as below:</p>
  
  <p><img src="https://i.stack.imgur.com/4qroG.png" alt="enter image description here"></p>
  
  <p>What I would like to do is create a new column in my data called 'CurrentValue' that would be a calculation of every TotalCost value based on the Transaction Date being in the current month.</p>
  
  <p>Ideally this would change as I changed into a new month going forwards.</p>
  
  <p>An example of this is the below image:-</p>
  
  <p><img src="https://i.stack.imgur.com/AjIcg.png" alt="enter image description here"></p>
  
  <p>where CurrentValue represents the Current Months figures.</p>