Visto en http://rm-rf.es/limitar-recursos-por-usuario-en-mysql/ :
CREATE USER 'usuario'@'localhost' IDENTIFIED BY 'elpassword'; GRANT ALL ON test.* TO 'prueba'@'localhost' WITH MAX_QUERIES_PER_HOUR 100 MAX_UPDATES_PER_HOUR 50 MAX_CONNECTIONS_PER_HOUR 100 MAX_USER_CONNECTIONS 20;
GRANT USAGE ON *.* TO 'prueba'@'localhost' WITH MAX_QUERIES_PER_HOUR 50;
GRANT USAGE ON *.* TO 'prueba'@'localhost' WITH MAX_QUERIES_PER_HOUR 0;
FLUSH USER_RESOURCES; FLUSH PRIVILEGES;