Convert Epoch to DateTime SQL Server (Exceeds Year 2038) - sql-server

Question

How to convert Epoch to DateTime SQL Server if epoch exceeds the year 2038?
Answer in Convert Epoch to DateTime SQL Server will not work.
Example:
SELECT DATEADD(ss, 2713795200000 / 1000, '19700101')
Thu, 30 Dec 2055 16:00:00 GMT

Answer 1

DATEADD function assumes an INT as an increment to your date, to bypass the limitation of INT you can either reduce the precision of your epoch, or do a slightly complex code to retain the precision of your epoch.
This reduces the precision to minutes:
SELECT DATEADD(MINUTE,#YourEpoch/60/1000, '1/1/1970')
This one splits your epoch to days and milliseconds and then combines them in a datetime
CREATE FUNCTION [dbo].[fn_EpochToDatetime] (#Epoch BIGINT)
RETURNS DATETIME
AS
BEGIN
DECLARE #Days AS INT, #MilliSeconds AS INT
SET #Days = #Epoch / (1000*60*60*24)
SET #MilliSeconds = #Epoch % (1000*60*60*24)
RETURN (SELECT DATEADD(MILLISECOND, #MilliSeconds, DATEADD(DAY, #Days, '1/1/1970')))
END;
However, I'm not quite sure why the 2nd solution is not as precise as I expect it to be.

Answer 2

Building on the response above, the solution provided works but does not protect from trying to convert to a date that is out of bounds for SQL server.
create function dbo.unixTimestampConversion (
#unixTime bigInt
)
returns dateTime2(7)
as
begin
declare
#output dateTime2(7)
, #days int
, #ms int
, #x int = (1000 * 60 * 60 * 24)
;
set #days = #unixTime / #x
;
set #ms = #unixTime % #x
;
if (#unixTime < 32503593600000 and #unixTime > -2208988800000)
begin
set #output = dateAdd (millisecond, #ms, dateAdd (day, #days, '1/1/1970'))
;
end
;
else if (#unixTime <= -2208988800000)
begin
set #output = '1/1/1900'
;
end
;
else if (#unixTime >= 32503593600000)
begin
set #output = '12/31/2999'
;
end
;
return #output
;
end
;

Answer 3

You can assign the epoch time to your datetime directly (I tried this on SQL Server 15.0). Although it considers the number as the number of days since 1900-1-1 00:00:00 so you have to add 2208988800 (the number of seconds in 70 years) and then divide by 86400(number of seconds in a day).
DECLARE #time DATETIME = (2208988800.0 + [your epoch time in seconds])/86400;
However, it seems to be 0.007s or 0.003s behind the given epoch. Also, I'm not sure if this is faster than the DATEADD() function.

Answer 4

create a function to convert epoch to datetime and use them in your query like
below
create FUNCTION [dbo].[from_unixtime] (#Datetime BIGINT)
RETURNS DATETIME
AS
BEGIN
DECLARE #LocalTimeOffset BIGINT
,#AdjustedLocalDatetime BIGINT;
SET #LocalTimeOffset = DATEDIFF(second,GETDATE(),GETUTCDATE())
SET #AdjustedLocalDatetime = #Datetime - #LocalTimeOffset
RETURN (SELECT DATEADD(second,#AdjustedLocalDatetime, CAST('1970-01-01 00:00:00' AS datetime)))
END;
and then use this function in your query