Comments on: Comparing date truncations

By: scott2718281828

scott2718281828 — Thu, 11 Sep 2008 00:50:20 +0000

To time the date operations alone, you should use a SET command that truncates a date variable instead of a SELECT to avoid any influence from I/O or cache. Put it in a loop that executes a million times, then subtract the time for an empty loop.

I’ve always found the dateadd/datediff method to be fastest. It only requires moving a 32-bit integer. Casting to a float is a little slower as it requires floating point arithmetic. Converting to character is terrible as it requires allocating and garbage collecting millions of string objects.

By: Gail

Gail — Tue, 09 Sep 2008 19:28:31 +0000

What kind of numbers did you get?

I can see the dateadd and the cast to float coming out in a different order. They were close in both CPU and execution time.

One thing I did notice (and should have mentioned) is that I forced a MAXDOP 1 on all of the queries when I ran them, as some were running parallel and some were not. I noticed that the parallel plans were significantly slower than the serial plans. Try that, see if it changes things.

By: DavidB

DavidB — Tue, 09 Sep 2008 16:24:21 +0000

Interesting in that my results turned out differently (same table and data as you) as follows;

1. Cast to float to floor
2. Cast to Date
3. DateAdd and Datediff
4. Cast to varchar (sadly this performed as poorly as yours)

So, with that being said, I don’t believe environment should make that much of a difference (dual core laptop with a bunch of memory running 2008). Curious if you have any thoughts why the disparity.

By: Gail

Gail — Sun, 07 Sep 2008 11:10:07 +0000

It works in 2008. Won’t work with the datetime2 data type though. But then neither does the method that casts to float.

On the same test box as the others, that one came in at:
CPU time 356ms, execution time 7994 ms

By: Peso

Peso — Sun, 07 Sep 2008 10:00:32 +0000

Same duration, slightly less CPU.
However I think it will not work on SQL Server 2008.

SELECT CAST(CAST(DateValue – 0.50000004 AS INT) AS DATETIME)
FROM #DateTest
GO 4