MSSQL bigint Unix Timestamp to Datetime with milliseconds

Question

I have some timestamps that are in bigint. Here's one:

1462924862735870900

This is down to microsecond precision.

I am currently using this:

SELECT DATEADD(S, CONVERT(int,LEFT(1462924862735870900, 10)), '1970-01-01')

That's giving me datetime down to the second but I would like to maintain at least millisecond precision.

I realize that DATEADD cannot handle bigint that's why I truncated the bigint and converted it to int. If I don't do that I get this error:

Arithmetic overflow error converting expression to data type int

I'm hoping someone can help me figure out a better way to convert this and maintain at least millisecond precision.

Any help would be greatly appreciated. Thanks!

---- UPDATE ------

With the help of @ako, I threw together a function that takes a bigint timestamp in either milliseconds, microseconds or nanoseconds and returns DATETIME2(7) which is 100 nanosecond precision. It could probably be more efficient but here's the function:

CREATE FUNCTION [dbo].[fn_tsConvert] (@ts bigint)
RETURNS DATETIME2(7)
AS BEGIN
    DECLARE @ts2 DATETIME2(7)

    -- MILLISECOND
    IF(LEN(@ts) = 13)
        SET @ts2 = DATEADD(HH,-4,DATEADD(MILLISECOND, @ts % 1000, DATEADD(SECOND, @ts / 1000, CAST('1970-01-01' as datetime2(7)))))

    -- MICROSECOND  
    IF(LEN(@ts) = 16)
        SET @ts2 = DATEADD(HH,-4,DATEADD(MICROSECOND, @ts % 1000000, DATEADD(SECOND, @ts / 1000000, CAST('1970-01-01' as datetime2(7)))))

    -- NANOSECOND   
    IF(LEN(@ts) = 19)
        SET @ts2 = DATEADD(HH,-4,DATEADD(NANOSECOND, @ts % 1000000000, DATEADD(SECOND, @ts / 1000000000, CAST('1970-01-01' as datetime2(7)))))

    RETURN @ts2

END

Answer 1

I think that you are dealing with nanosecond precision. What you can get in native sql is 100ns precision.

declare @ts as bigint = 1462924862735870900

select dateadd(NANOSECOND, @ts % 1000000000, dateadd(SECOND, @ts / 1000000000, cast('1970-01-01' as datetime2(7))))

The outcome is 2016-05-11 00:01:02.7358709