Best approach to remove time part of datetime in SQL Server
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()), 0)
or
b) select cast(convert(char(11), getdate(), 113) as datetime)
The second method does send a few more bytes either way but that might not be as important as the speed of the conversion.
Both also appear to be very fast, but there might be a difference in speed when dealing with hundreds-of-thousands or more rows?
Also, is it possible that there are even better methods to get rid of the time portion of a datetime in SQL?
Strictly, method a is the least resource intensive:
a) select DATEADD(dd, DATEDIFF(dd, 0, getdate()), 0)
Proven less CPU intensive for same total duration a million rows by some one with way too much time on their hands: Most efficient way in SQL Server to get date from date+time?
I saw a similar test elsewhere with similar results too.
I prefer the DATEADD/DATEDIFF because:
Example: Why is my CASE expression non-deterministic?
Edit, Oct 2011
For SQL Server 2008+, you can CAST to date . Or just use date so no time to remove.
Edit, Jan 2012
A worked example of how flexible this is: Need to calculate by rounded time or date figure in sql server
Edit, May 2012
Do not use this in WHERE clauses and the like without thinking: adding a function or CAST to a column invalidates index usage. See number 2 here: http://www.simple-talk.com/sql/t-sql-programming/ten-common-sql-programming-mistakes/
Now, this does have an example of later SQL Server optimiser versions managing CAST to date correctly, but generally it will be a bad idea ...
在SQL Server 2008中，您可以使用：
CONVERT(DATE, getdate(), 101)
Of-course this is an old thread but to make it complete.
From SQL 2008 you can use DATE datatype so you can simply do:
SELECT CONVERT(DATE,GETDATE())
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