title: A way to have a rolling summation
body: <p>I have the below dataset. In the below example records for the year 1993. The <code>Tgrowth</code> column is <code>start - end</code>. <code>Started</code> is the number of employees that joined on a specific month and <code>ended</code> is the number of employees that left for the same month.</p>
  <p><a href="https://i.stack.imgur.com/9EcWs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9EcWs.png" alt="enter image description here" /></a></p>
  <pre><code>SELECT 
          r.Tgrowth,
              CASE
                  WHEN t.mon_num = 1 THEN 'JAN'
                  WHEN t.mon_num = 2 THEN 'FEB'
                  WHEN t.mon_num = 3 THEN 'MAR'
                  WHEN t.mon_num = 4 THEN 'APR'
                  WHEN t.mon_num = 5 THEN 'MAY'
                  WHEN t.mon_num = 6 THEN 'JUN'
                  WHEN t.mon_num = 7 THEN 'JUL'
                  WHEN t.mon_num = 8 THEN 'AUG'
                  WHEN t.mon_num = 9 THEN 'SEP'
                  WHEN t.mon_num = 10 THEN 'OCT'
                  WHEN t.mon_num = 11 THEN 'NOV'
                  WHEN t.mon_num = 12 THEN 'DEC'
              END AS myMONTH
      FROM
          (SELECT 1 mon_num UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION SELECT 9 UNION SELECT 10 UNION SELECT 11 UNION SELECT 12) t
      LEFT JOIN Reports r ON t.mon_num = r.theMONTH
          AND r.Tyear = 1993
      GROUP BY r.Tgrowth , myMONTH
      ORDER BY t.mon_num ASC
  </code></pre>
  <p>The result set for the above is as follows,</p>
  <pre><code>Tgrowth Month
  1      JAN
  0      FEB
  2      MAR
  0      APR
  0      MAY
  0      JUN
  0      JUL
  0      AUG
  0      SEP
  0      OCT
  0      NOV
  0      DEC
  </code></pre>
  <p>Instead I would like the result to show a rolling sum i.e. add to the <code>Tgrowth</code> field. Something like the below,</p>
  <pre><code>growth  Emp_Count   myMONTH
  1          1        JAN
  0          1        FEB
  2          3        MAR
  0          3        APR
  0          3        MAY
  0          3        JUN
  0          3        JUL
  0          3        AUG
  0          3        SEP
  0          3        OCT
  0          3        NOV
  0          3        DEC
  </code></pre>