update prenomina_rpt
set (HEXRAS) =
(select NVL(sum(ve.duracion/60),0)
from empleados_seleccion es,
v_eventos_periodo_horas ve,
eventos e
where es.id_seleccion = p_id_seleccion
and es.empleado = v_empleado
and es.id_empleado = ve.id_empleado
and ve.fecha_aplicacion >= p_fechadesde
and ve.fecha_aplicacion <= p_fechahasta
and e.id_evento = 3
and e.id_evento = ve.id_evento
group by ve.id_empleado, e.clave_evento);

can somebody help me to make this update works?.
this works fine when i have one record in empleados_seleccion table, but when this table have more than one record update HEXRAS whit the same value.
thanks in advance