title: How to find the cumulative salary with each year?
body: <p>The output should be the last column (Cum_Sal).</p>
  
  <pre><code> EMPLOYEE   MONTH   YEAR    SALARY Cum_Sal
   A            JAN   2016    2000     2000
   A            FEB   2016    2000     4000
   A            MAR   2016    2000     6000
   A            APR   2016    3000     9000
   A            MAY   2016    3000     12000
   A            JUN   2016    3000     15000
   A            JUL   2016    3000     18000
   A            AUG   2016    3000      .
   A            SEP   2016    3000       .
   A            OCT   2016    3000
   A            NOV   2016    3000
   A            DEC   2016    3000
   A            JAN   2017    3000     3000
   A            FEB   2017    3000     6000
   A            MAR   2017    3000     9000
   A            APR   2017    5000      .
   A            MAY   2017    5000       . (SO ON)
   A            JUN   2017    5000
   A            JUL   2017    5000
   A            AUG   2017    5000
  </code></pre>
  
  <p>Thanks for your help.
  SM</p>