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

Here is a slightly different approach that I used when I needed to round down to the nearest 5 minute interval. There is probably a way to simplify this further, but at least this got me what I needed.

DECLARE @now datetime = GETDATE()

SELECT @now as cur_datetime, DATEADD(MINUTE, -(DATEDIFF(MINUTE,DATEADD(HOUR,DATEDIFF(HOUR,0,@now), 0),DATEADD(MINUTE,DATEDIFF(MINUTE,0,@now), 0)) % 5), DATEADD(MINUTE,DATEDIFF(MINUTE,0,@now), 0)) as round_down_to_nearest_5_minute_mark