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

Just in case anyone is looking in here for a Sybase version since several of the versions above didn't work

CAST(CONVERT(DATE,GETDATE(),103) AS DATETIME)

• Tested in I SQL v11 running on Adaptive Server 15.7

Answer 2

Here I made a function to remove some parts of a datetime for SQL Server. Usage:

• First param is the datetime to be stripped off.
• Second param is a char:
  • s: rounds to seconds; removes milliseconds
  • m: rounds to minutes; removes seconds and milliseconds
  • h: rounds to hours; removes minutes, seconds and milliseconds.
  • d: rounds to days; removes hours, minutes, seconds and milliseconds.
• Returns the new datetime

create function dbo.uf_RoundDateTime(@dt as datetime, @part as char) returns datetime as begin if CHARINDEX( @part, 'smhd',0) = 0 return @dt; return cast( Case @part when 's' then convert(varchar(19), @dt, 126) when 'm' then convert(varchar(17), @dt, 126) + '00' when 'h' then convert(varchar(14), @dt, 126) + '00:00' when 'd' then convert(varchar(14), @dt, 112) end as datetime ) end

Answer 3

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:

• varchar is subject to language/dateformat issues
  Example: Why is my CASE expression non-deterministic?
• float relies on internal storage
• it extends to work out first day of month, tomorrow etc by changing "0" base

Edit, Oct 2011

For SQL Server 2008+, you can CAST to date i.e. CAST(getdate() AS date). Or just use date datatype 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 ...

Edit, Sep 2018, for datetime2

DECLARE @datetime2value datetime2 = '02180912 11:45' --this is deliberately within datetime2, year 0218
DECLARE @datetime2epoch datetime2 = '19000101'

select DATEADD(dd, DATEDIFF(dd, @datetime2epoch, @datetime2value), @datetime2epoch)

Answer 4

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())

Answer 5

If possible, for special things like this, I like to use CLR functions.

In this case:

[Microsoft.SqlServer.Server.SqlFunction]
    public static SqlDateTime DateOnly(SqlDateTime input)
    {
        if (!input.IsNull)
        {
            SqlDateTime dt = new SqlDateTime(input.Value.Year, input.Value.Month, input.Value.Day, 0, 0, 0);

            return dt;
        }
        else
            return SqlDateTime.Null;
    }

Answer 6

In SQL Server 2008, you can use:

CONVERT(DATE, getdate(), 101)