title: How to separate sum() of positive and negative numbers into other rows
body: <p>table1</p>
  
  <pre><code>-------------
  |  a  |  b  |
  -------------
  | -1 |  1  |
  |  5 |  3  |
  | -4 | -4  |
  |  6 |  7  |
  |  9 | -2  |
  -------------
  </code></pre>
  
  <p>Answer</p>
  
  <pre><code>negative :
  positive :
  </code></pre>
  
  <p><strong>EDIT:</strong></p>
  
  <p>It's a special condition to not use <code>union</code>.</p>