Mendapatkan jumlah hasil dateiff

Jika Anda menyertakan kolom lain, Anda juga harus menyertakan klausa GROUP BY

SELECT     AnotherColumn, SUM(DATEDIFF(day, StartDate, EndDate)+1) AS myTotal
FROM         myTable
WHERE      (Reason = '77000005471247')
GROUP BY   AnotherColumn