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

@Twinkles's answer works well in SQL server to round to closest half an hour.

However, in development, strongly recommend use FLOOR to round to last half an hour.

SELECT CONVERT(datetime, FLOOR(CAST([columnname] AS float) * 48.0)/48.0) FROM [tableName]

Answer 2

The answer by Ian is good, but it contains an unnecessary conversion. I suggest

SELECT CONVERT(smalldatetime, ROUND(CAST([columnname] AS float) * 48.0,0,1)/48.0) FROM [tableName]

If you want to round to the nearest half-hour instead of always rounding down, use

SELECT CONVERT(smalldatetime, ROUND(CAST([columnname] AS float) * 48.0,0)/48.0) FROM [tableName]

Answer 3

How about this

declare @d datetime = '2013-05-06 12:29.123'
select 
case 
    when datepart(minute, @d) < 30 then cast(dateadd(minute, -datepart(minute,@d)-datepart(second,@d), @d) as smalldatetime)
    when datepart(minute, @d) >= 30 then cast(dateadd(minute, -datepart(minute,@d)-datepart(second,@d)+30, @d) as smalldatetime)
end

Answer 4

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

Answer 5

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)

Answer 6

Here is one way to do it:

update t set
  d = dateadd(minute,datediff(minute,'19000101',d)/30*30,'19000101');