mssql 2008 datediff与分钟

Question

我正在使用这个：

DECLARE @startdate datetime2 = '08:00:00.000';
DECLARE @enddate datetime2 = '08:04:21.000'; 
SELECT DATEDIFF(minute, @startdate, @enddate) as minute; 

我得到了输出 分钟：4

但是当我在下面输入时：

DECLARE @startdate datetime2 = '08:00:00.000';
DECLARE @enddate datetime2 = '07:59:21.000'; 
SELECT DATEDIFF(minute, @startdate, @enddate) as minute; 

然后我得到输出：-1

所以我不想要输出：-1。它必须是空白的输出

谢谢

Answer 1

您可以使用CASE语句应用if @startdate is greater than @enddate then null else datediff

等逻辑

SELECT CASE WHEN @startdate > @endate THEN NULL 
       ELSE DATEDIFF(minute, @startdate, @endate) END