title: Oracle sum previous values
body: <p>I´m trying to do the the following: With this table:</p>
  
  <pre><code>DATE       VAR       
  ---------------
   2011      2.82          
   2012     -3.47        
   2013     -5.8        
   2014      13
  </code></pre>
  
  <p>I need to obtain this other table:</p>
  
  <pre><code> DATE    VAR       ACUM    
  ---------------------------------------
   2011    2.82         
   2012   -3.47     -0.65      
   2013   -5.8      -6.45      
   2014    13        6.55 
  </code></pre>
  
  <p>i.e. i nedd another column with the VAR value plus the sum of the all previous values.</p>
  
  <pre><code>for the 2014 row....13-5.8-3.47+2.82 = 6.55
  for the 2013 row....-5.8-3.47+2.82 = -6.45
  </code></pre>
  
  <p>and so on.</p>