Recurso interessante e muito util do MySQL que até então eu desconhecia.
[SQL]
INSERT INTO Sales(TransId, Status, Amount)
VALUES(123, ‘Pending’, 20)
ON DUPLICATE KEY UPDATE Status = ‘Paid’
[/SQL]
Fonte:
http://thingsilearn.wordpress.com/2007/10/29/mysql-insert-or-update-in-one-query/
http://particletree.com/notebook/to-insert-or-to-update/
http://dev.mysql.com/doc/refman/5.1/en/insert-on-duplicate.html