Hello! I'm running this query: SELECT DISTINCT CONCAT(ALFA_CLAVE, FECHA_NACI) FROM listado GROUP BY ALFA_CLAVE HAVING count(CONCAT(ALFA_CLAVE, FECHA_NACI)) > 1 Is there any way to optimize it? Queries are taking 2-3 hours on a table with 850,000 rows. Adding an index to ALFA_CLAVE and FECHA_NACI would work? Thanks in advanced