Truncate Datetime to Second (Remove Milliseconds) in T-SQL

Question

What is the best way to shorten a datetime that includes milliseconds to only have the second?

For example 2012-01-25 17:24:05.784 to 2012-01-25

Answer 1

Expanding on accepted answer by @Mikael Eriksson:

To truncate a datetime2(7) to 3 places (aka milliseconds):

   -- Strip of fractional part then add desired part back in
   select dateadd(nanosecond,
                  -datepart(nanosecond, TimeUtc) + datepart(millisecond, TimeUtc) * 1e6,
                  TimeUtc) as TimeUtc

The current max precision of datetime2(p) is (7) (from docs.microsoft.com)

Answer 2

convert(datetime, convert(varchar, @datetime_var, 120), 120)