Convert seconds to datetime in SQL Server

Question

How to convert seconds to datetime? I try this, but results are not correct:

CONVERT(datetime, DATEADD(ms, dateTimeInSeconds, 0))

Answer 1

When you use the value zero for date, this is converted to 1900-01-01. Use the specific date that you have selected as epoch:

convert(datetime, dateadd(ms, dateTimeInMilliseconds, '2010-01-01'))

Note that the datetime data type doesn't have millisecond precision, the resolution is 1/300 second. If you for example have four milliseconds and convert it, you get 2010-01-01 00:00:00.003 rather than 2010-01-01 00:00:00.004. If you need to preserve the millisecond resolution, you need to use the datetime2 data type:

convert(datetime2, dateadd(ms, dateTimeInMilliseconds, cast('2010-01-01' as datetime2)))

Edit:

To use seconds instead of milliseconds, use s instead of ms in the dateadd call:

convert(datetime, dateadd(ms, dateTimeInSeconds, '1970-01-01'))