Mi chiedo: l'unica soluzione è due query una dentro l'altra?

SELECT id,cognome,nome,localita_id FROM fusion_clienti

if (localita_id != NULL) {

SELECT fusion_province.id AS FUSION_PROVINCE_ID,
fusion_province.provincia AS FUSION_PROVINCE_PROVINCIA,
fusion_comuni.id AS FUSION_COMUNI_ID,
fusion_comuni.comune AS FUSION_COMUNI_COMUNE,
fusion_comuni.provincia_id AS FUSION_COMUNI_PROVINCIA_ID,
fusion_localita.id AS FUSION_LOCALITA_ID,
fusion_localita.localita AS FUSION_LOCALITA_LOCALITA,
fusion_localita.comune_id AS FUSION_LOCALITA_COMUNE_ID,
fusion_localita.cap AS FUSION_LOCALITA_CAP,
FROM
fusion_province,
fusion_comuni,
fusion_localita
WHERE (fusion_province.id = fusion_comuni.provincia_id)
and (fusion_comuni.id = fusion_localita.comune_id)
ORDER BY fusion_province.provincia ASC,
fusion_comuni.comune ASC,
fusion_localita.localita ASC
}