title: sql: delete a subtree table(id, Parentid) , delete a item with all his children
body: <p>I have a table like this </p>
  
  <pre><code>foo(id, parentId) 
  -- there is a FK constraint from parentId to id
  </code></pre>
  
  <p>and I need to delete an item with all his children and children of the children etc.
  anybody knows how ?</p>