Prueba asi:
Código SQL:
Ver originalSELECT id_linia_incidencia, COUNT(1)
FROM (
SELECT DISTINCT identificador, id_linia_incidencia
FROM NSG_INCIDENCIES_CLIENT C
INNER JOIN NSG_INCIDENCIES_HISTORIC H ON C.id_incidencia = H.id_incidencia
WHERE YEAR(data_incidencia)='2010' AND DAY(data_incidencia)='14'
) T
GROUP BY id_linia_incidencia