title: how to allow different inputs only from the same 'number'
body: <p>I do not want to register repeated <code>msg</code> from the same <code>number</code>, but if there adds to <code>dup</code> counter</p>
  
  <pre><code>INSERT INTO sms (number, msg) 
    VALUES (%s, %s)
    ON DUPLICATE KEY UPDATE dup = dup+1
  </code></pre>
  
  <p>how to allow different inputs only from the same <code>number</code>?</p>