Best approach to remove time part of datetime in SQL Server

Question

Which method provides the best performance when removing the time portion from a datetime field in SQL Server?

a) select DATEADD(dd, DATEDIFF(dd, 0, getdate(         


        

Answer 1

I think you mean cast(floor(cast(getdate()as float))as datetime)

real is only 32-bits, and could lose some information

This is fastest cast(cast(getdate()+x-0.5 as int)as datetime)

...though only about 10% faster(about 0.49 microseconds CPU vs. 0.58)

This was recommended, and takes the same time in my test just now: DATEADD(dd, DATEDIFF(dd, 0, getdate()), 0)

In SQL 2008, the SQL CLR function is about 5 times faster than using a SQL function would be, at 1.35 microseconds versus 6.5 microsections, indicating much lower function-call overhead for a SQL CLR function versus a simple SQL UDF.

In SQL 2005, the SQL CLR function is 16 times faster, per my testing, versus this slow function:

create function dateonly (  @dt datetime )
returns datetime
as
begin
return cast(floor(cast(@dt as float))as int)
end