title: txn_id and payment_status makes PayPal IPN unique?
body: <p>I'm working with PayPal IPN and I have the following question: Is it possible, to have two IPN messages with the same txn_id and payment_status parameter?</p>
  
  <p>For example:</p>
  
  <ol>
  <li>IPN: txn_id=4BB79227HY951745W&amp;payment_status=pending</li>
  <li>IPN: txn_id=4BB79227HY951745W&amp;payment_status=idontknowwhat</li>
  <li>IPN: tnx_id=4BB79227HY951745W&amp;payment_status=pending</li>
  <li>IPN: txn_id=4BB79227HY951745W&amp;payment_status=completed</li>
  </ol>
  
  <p>So my question is basically that the txn_id and the payment_status together make the messages unique, or not?</p>
  
  <p>Another example:</p>
  
  <p>If I have an SQL query like: </p>
  
  <p>SELECT * FROM transactions WHERE txn_id=4BB79227HY951745W AND payment_status=something </p>
  
  <p>Can it returns with more than one rows? (If I don't store any messages re-sent by PayPal because of the lack of 200 OK response message or slow response time or anything like this.)</p>
  
  <p>I read this thread before: <a href="https://stackoverflow.com/questions/9240235/paypal-ipn-unique-identifier">PayPal IPN unique identifier</a> . Here it sounds that these two parameters make the message unique, but i'm not sure.</p>