title: Optimize SELECT DISTINCT CONCAT query in MySQL
body: <p>I'm running this query:</p>
  
  <pre><code>SELECT DISTINCT CONCAT(ALFA_CLAVE, FECHA_NACI) FROM listado GROUP BY ALFA_CLAVE HAVING count(CONCAT(ALFA_CLAVE, FECHA_NACI)) &gt; 1
  </code></pre>
  
  <p>Is there any way to optimize it? Queries are taking 2-3 hours on a table with 850,000 rows.</p>
  
  <p>Adding an index to ALFA_CLAVE and FECHA_NACI would work?</p>