Convert specific BigInt to DateTime in T-SQL

Question

I have bigInt: 635307578922100000 which I need to convert to DateTime.

I've tried few ways to do this:

SELECT 
    DATEADD(S, CONVERT(bigint,635307578922100000) / 1000, CONVERT(DATETIME, '1-1-1970 00:00:00')) 

and:

SELECT 
    DATEADD(ms, 635307578922100000 / 86400000, (635307578922100000 / 86400000) +25567)

While I found the codes above work with bigInts like: 1283174502729, with my bigInt I get the following error:

Msg 8115 ... Arithmetic overflow error converting expression to data type datetime.

Does anyone have any idea how to solve it?

Answer 1

Here are some calculations that can calculate the bigint to a datetime.

SELECT
tick.value

-- Subtrack the amount of ticks for 1900-01-01 and divide that number by the ticks in 1 day.
-- Then cast or convert that smaller number to a datetime
-- But only accurate to the second.
-- 864000000000 = (10000000 * 24 * 60 * 60)
 , CAST((tick.value - 599266080000000000) / 864000000000 AS datetime) as DateTimeCalc1

-- Subtrack the amount of ticks for 1900-01-01 and divide by the ticks in 1 minute.
-- Then add that smaller number as minutes to 1900-01-01
-- Only accurate to the minute
 , DATEADD(MINUTE, ((tick.value - 599266080000000000) / 600000000), CAST('1900-01-01' AS DATETIME)) as DateTimeCalc2

-- Same method as for DateTimeCalc2, but include the milliseconds.
-- Accurate to the millisecond
 , DATEADD(MILLISECOND, FLOOR((((tick.value - 599266080000000000)/10000)%60000)), DATEADD(MINUTE, FLOOR((tick.value - 599266080000000000)/600000000), CAST('1900-01-01' AS DATETIME))) as DateTimeCalc3

FROM (values 
  (convert(bigint,635307578922100000))
 ,(convert(bigint,599266080000000000))
 ,(convert(bigint,630823257457000000))
 ,(convert(bigint,646602048000000000))
) AS tick(value);

Result:

value               DateTimeCalc1           DateTimeCalc2           DateTimeCalc3
------------------ ----------------------- ----------------------- -----------------------
635307578922100000 2014-03-18 16:44:52.207 2014-03-18 16:44:00.000 2014-03-18 16:44:52.210
599266080000000000 1900-01-01 00:00:00.000 1900-01-01 00:00:00.000 1900-01-01 00:00:00.000
630823257457000000 2000-01-01 12:15:45.697 2000-01-01 12:15:00.000 2000-01-01 12:15:45.700
646602048000000000 2050-01-01 00:00:00.000 2050-01-01 00:00:00.000 2050-01-01 00:00:00.000

With a bit of tampering those datetimes can be truncated or rounded on the seconds.

SELECT tick.value

-- Truncated
, CAST(CONVERT(varchar, CAST((tick.value - 599266080000000000) / 864000000000 AS datetime),20) AS datetime) as DateTimeTruncated

-- Rounded
, CAST(CAST(CAST((tick.value - 599266080000000000) / 864000000000 AS datetime) as datetime2(0)) AS datetime) as DateTimeRounded

-- For dates between 1981-12-14 and 2118-01-19, one could add seconds to 2050-01-01. 
, DATEADD(SECOND, ((tick.value - 646602048000000000) / 10000000), cast('2050-01-01' as datetime)) as DateTimeSecondsAdded

FROM (values 
(630823257457000000),
(635307578922100000),
(662380857456770000)
) tick(value);

Answer 2

I think it's in ticks (yields 2014-03-18 16:44:52.210). Here is solution:

SELECT DATEADD(
    MILLISECOND,
    FLOOR(((635307578922100000-599266080000000000)%(10000000*60))/10000),
    DATEADD(
        MINUTE,
        FLOOR((635307578922100000-599266080000000000)/(10000000*60)),
        '01-01-1900'))

This magic value 599266080000000000 is number of ticks between 0001-01-01 and 1900-01-01 calculated in PowerShell as follows:

([DateTime]::Parse('1900-01-01')-[DateTime]::MinValue).Ticks

Conversions are required, because DATEADD won't work with bigint (requires int). SQL Server DateTime is also limited to 1 January 1753.