关键是要使用DATEADD 和 DATEDIFF 以及相应的 SQL时间跨度枚举.

The key is to use DATEADD and DATEDIFF along with the appropriate SQL timespan enumeration.

declare @datetime datetime;
set @datetime = getdate();
select @datetime;
select dateadd(year,datediff(year,0,@datetime),0);
select dateadd(month,datediff(month,0,@datetime),0);
select dateadd(day,datediff(day,0,@datetime),0);
select dateadd(hour,datediff(hour,0,@datetime),0);
select dateadd(minute,datediff(minute,0,@datetime),0);
select dateadd(second,datediff(second,'2000-01-01',@datetime),'2000-01-01');
select dateadd(week,datediff(week,0,@datetime),-1); --Beginning of week is Sunday
select dateadd(week,datediff(week,0,@datetime),0); --Beginning of week is Monday

请注意，当您按秒计算时，如果使用 0，通常会出现算术溢出.因此请选择一个已知值，该值保证低于您尝试计算的日期时间.

Note that when you are flooring by the second, you will often get an arithmetic overflow if you use 0. So pick a known value that is guaranteed to be lower than the datetime you are attempting to floor.