title: oracle sql detect changes in subquery
body: <p>Hello i need to detect changes in a table.
  To be more specific i need to detect changes in a subquery.</p>
  
  <p>Lets say i have a user Table FOO with a key persnr</p>
  
  <pre><code>select distinct persnr,(select max(ora_rowscn) 
  from FOO where persnr = A.persnr) from FOO A
  order by persnr;
  </code></pre>
  
  <p>But as far as i know the ora_rowscn pseudocolumn is not very precise.
  And that is what i experienced. When i change rows for a specific persnr
  the ora_rowscn might be the same on various rows even with a different persnr.</p>
  
  <p>how can i detect changes on a specific persnr ?</p>