Rounding a datetime value down to the nearest half hour

Question

I have a requirement to round a datetime2 value down to the nearest half hour. For example \'10/17/2013 12:10:00.123\' would round down to \'10/17/2013 12:00:00.0\' And \'10

Answer 1

select cast(floor(cast(
    cast('10/17/2013 12:34:00' as datetime) 
as float(53)) * 48) / 48 as datetime)

EDIT

Works better if you use smalldatetime to avoid the extra precision

select cast(floor(cast(
    cast('2012-01-02 11:33:14.097' as smalldatetime) 
as float(53)) * 48) / 48 as smalldatetime)