SELECT 
YEAR(T1.EVT_TARGET) AS anno, 
MONTH(T1.EVT_TARGET) AS mese, 
T1.EVT_JOBTYPE,
T2.prv_code, 
DateDiff(hh,
(select T3.prv_dvalue from R5PROPERTYVALUES AS T3 where (T3.PRV_PROPERTY = 'UTNCIN' AND T3.prv_code = T2.prv_code)),
(select T4.prv_dvalue from R5PROPERTYVALUES AS T4 where (T4.PRV_PROPERTY = 'UTNCOUT' AND T4.prv_code = T2.prv_code))
) AS Differ
FROM R5EVENTS AS T1
INNER JOIN
dbo.R5PROPERTYVALUES AS T2 
ON 
T2.PRV_CODE = T1.EVT_CODE 
GROUP BY 
YEAR(T1.EVT_TARGET), MONTH(T1.EVT_TARGET), T2.prv_code, T1.EVT_JOBTYPE