title: How to calculate arithmetic expression of column members database table?
body: <p>I have result from this query</p>
  
  <pre><code>SELECT
      myTable.Branch AS Branch,
      myTable.Quarter AS Quarter,
      SUM(myTable.Sales) AS Sales
  FROM
      myTable
  GROUP BY
      myTable.Branch,
      myTable.Quarter
  
  Branch  Quarter Sales
  B1      Q1      17
  B1      Q2      7
  B1      Q3      1
  B1      Q4      8
  B1      Q5      12
  B2      Q1      8
  B2      Q2      5
  B2      Q3      2
  B2      Q4      14
  B2      Q5      17
  </code></pre>
  
  <p>Now I want to get calculate member lets say <code>Q1-Q3</code> then result should look like</p>
  
  <pre><code>Branch  Quarter     Sales
  B1      Q1          17
  B1      Q2          7
  B1      Q3          1
  B1      Q4          8
  B1      Q5          12
  B1      Q1-Q3       16
  B2      Q1          8
  B2      Q2          5
  B2      Q3          2
  B2      Q4          14
  B2      Q5          17
  B2      Q1-Q3       6
  </code></pre>
  
  <p>Expression can be any valid arithmetic expression like <code>(Q1+Q2-Q3)*2</code></p>