title: How to select lowest level in hierarchy from table
body: <p>I have a table with parent/child relationship:</p>
  
  <pre><code>Table A
  Column Id int
  Column Parent_Id int
  Column Description text
  </code></pre>
  
  <p>An example set of data would be:</p>
  
  <pre><code>999, NULL, 'Corp.'
  998, 999, 'Div1',
  997, 999, 'Div2', 
  510, 998, 'Child Div1A',
  110, 997, 'Child Div2A',
  120, 997, 'Child Div2B',
  </code></pre>
  
  <p>My query needs to return the lowest set of children, given a parent. So, for example, if given 999, I would return 510, 110, 120. But given 997, I would return only 110 and 120. If given 110, nothing would return. I can't figure out how to format my query quite correctly. I started by JOIN-ing the table on itself, but it seems like that would only get me 1 level down when I actually neeed to go N-levels down.</p>