Jeffrey Williams 3188 (5/8/2013)

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Michael Valentine Jones (5/8/2013)

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select

DT,

SecondsSince_19000101 =

-- seconds for whole days as bigint

(datediff(dd,0,a.DT)*000000000086000)+

-- seconds since start of day

datediff(ss,dateadd(dd,datediff(dd,0,a.DT),0),a.DT)

from

( -- test data

select DT = getdate()union all

select DT = '99991231 23:59:59.997'union all

select DT = '18991231 12:01:01.997'union all

select DT = '17530101 00:00:00.000'

) a

order by

a.DT

Results:

DT SecondsSince_19000101

----------------------- ---------------------

1753-01-01 00:00:00.000 -4617340000

1899-12-31 12:01:01.997 -42739

2013-05-08 13:35:03.717 3560448903

9999-12-31 23:59:59.997 254427904399

Michael, can you explain why you used 86000 instead of 86400? There are 86,400 seconds in a day - and it appears your calculation will be off because of that.