Convert .NET Ticks to SQL Server DateTime

Question

I am saving a TimeSpan (from .NET) value in my db as BIGINT in SQL Server (saving the Ticks property). I want to know how to convert this BIGINT value to a DATETIME value in SQL Server (not in .NET). Any ideas?

Cheers

EDIT:

I am using NHibernate to map a TimeSpan property I have, and it persists the Ticks property. I use it for relative hours (or minutes) control over some date.

Internally in the system everything is fine, this conversion isn't needed. However, when performing random queries in SQL Server, it is hard to understand the persisted form of a TimeSpan. So, a function where I pass the Ticks value and a DateTime is returned would give the amount in hours, minutes and seconds that that TimeSpan represents.

Answer 1

I don't really know SQL Server, but today a colleague of mine had the same problem and I think I've found a solution like this:

CAST(([ticks] - 599266080000000000) / 10000000 / 24 / 60 / 60 AS datetime)

where 599266080000000000 is the ticks value for 01/01/1900 00:00:00.

Answer 2

I'm not sure how accurate this will be with the seconds, but you could try something like:

Declare @TickValue bigint
Declare @Days float

Set @TickValue = 634024345696365272 
Select @Days = @TickValue * POWER(10.00000000000,-7) / 60 / 60 / 24

Select DATEADD(d, Cast(@Days As int), Cast('0001-01-01' As DATE)) 
    + Cast( (@Days - FLOOR(@Days)) As DateTime)

Actually another way that would work in SQL 2005 is to note that the the number of ticks from 0001-01-01 to 1900-01-01 is 599266080000000000. With that you could do:

Declare @TickOf19000101 bigint
Declare @TickValue bigint
Declare @Minutes float

Set @TickOf19000101  = 599266080000000000
Set @TickValue = DATEDIFF(mi, 0 ,CURRENT_TIMESTAMP) * Cast(60 As BigInt) 
                   * POWER(10.00000000000,7) + @TickOf19000101

Select @TickValue
Select @Minutes = (@TickValue - @TickOf19000101) * POWER(10.00000000000,-7) / 60

Select @Minutes
Select DATEADD(MI, @Minutes, '1900-01-01')