title: How does a sub query in the from clause work?
body: <p>What is a valid use-case for Sub Query in the FROM clause? How does that scheme work? There are many examples of this type in SO. A link to one of those is <a href="https://stackoverflow.com/q/9025823/1527084">here</a> but I can't see how this scheme works.</p>
  
  <p>P.S: If the answer is Oracle specific it is fine.</p>