我的查询有问题吗？ （DATEDIFF）

Question

此查询应该用于获取在特定日期创建的学生数据。但是，如果我为@NumberOfDays输入15，它将返回15天和14天的数据，如果我输入20，这次它会带来19天和20天的数据。有人可以帮我解决我的疑问吗？我不知道我做错了什么。

SELECT TOP 10 S.Id, S.Name, S.Surname, S.DateCreated
FROM STUDENT S WITH(NOLOCK)
WHERE DATEDIFF(day, CAST(S.DateCreated AS date), CAST(GETDATE() AS date)) = @NumberOfDays

Answer 1

SELECT TOP 10 S.Id, S.Name, S.Surname, S.DateCreated
FROM STUDENT S WITH(NOLOCK)
WHERE DATEDIFF(day, CAST(S.DateCreated AS date), CAST(GETDATE() AS date)) 
Between @NumberOfDays-1 and @NumberOfDays

Answer 2

通过此查询，它最终有效！

SELECT TOP 10 S.Id, S.Name, S.Surname, S.DateCreated
FROM STUDENT S WITH(NOLOCK)
WHERE CAST(S.DateCreated AS DATE) = CAST(DATEADD(DAY, -@NumberOfDays, GETDATE()) AS DATE)