title: Insert a UNIQUE DUMMY COLUMN when creating VIEW with UNION
body: <p>I have a table with this structure:</p>
  
  <p><img src="https://i.stack.imgur.com/IJzJF.png" alt="enter image description here"></p>
  
  <p>I use this script to query the requests:</p>
  
  <pre><code>SELECT   D.DELIVERY_REQUEST_ID AS "REQUEST_ID",
           'Delivery' AS "REQUEST_TYPE"
     FROM  DELIVERY_REQUEST D
  UNION
  SELECT   I.INVOICE_REQUEST_ID AS "REQUEST_ID",
           'Invoice' AS "REQUEST_TYPE"
     FROM  INVOICE_TRX I
  </code></pre>
  
  <p>The result would be like this:</p>
  
  <pre><code>    REQUEST_ID    |    REQUEST_TYPE
  __________________|____________________
                    |
      1             |    Delivery
      1             |    Invoice
      2             |    Delivery
      2             |    Invoice
  </code></pre>
  
  <p>What I want to do is to query (or create a view) this with a unique key (should be an INT and like an auto number) at the beginning like this:</p>
  
  <pre><code>ID  |  REQUEST_ID    |    REQUEST_TYPE
  ____|________________|____________________
      |                |
  1   |  1             |    Delivery
  2   |  1             |    Invoice
  3   |  2             |    Delivery
  4   |  2             |    Invoice
  </code></pre>
  
  <p>Thank you in advance.</p>