title: SUMMING a conditional statement
body: <p>I have the following query that gives me the sum of sales:</p>
  
  <pre><code>SELECT SUM(sales)
  FROM 
      (SELECT sales FROM ...) combined
  </code></pre>
  
  <p>I now need to add a conditional subtraction based upon certain currencies that take out taxes, something like this, in pseudocode:</p>
  
  <pre><code>SELECT SUM(sales) - (SUM(sales) IF currency IN ('jpy', 'aud') * 0.05)
  FROM 
      (SELECT sales FROM ...) combined
  </code></pre>
  
  <p>How would I create this conditional SUM or subquery?</p>