title: How to Update tables based on self join
body: <p>Update table based on self join on customer_po = ID</p>
  
  <p><strong>Table XYZ</strong> </p>
  
  <pre><code>ID     Invoice Date   Delivery_date  Customer_po
  123    01-01-2018     null           null               
  125    10-01-2018     null           123
  </code></pre>
  
  <p>I want Output record like below in Oracle SQL</p>
  
  <pre><code>ID     Invoice Date   Delivery_date  Customer_po
  123    01-01-2018     01-01-2018     null
  125    10-01-2018     01-01-2018     123
  </code></pre>