How to Convert UNIX Timestamps to DateTime in SQL Server and Handle the Year 2038 Problem?

Converting UNIX Timestamps to Dates in SQL Server

Many SQL Server users need to convert UNIX timestamps (stored as bigint) into DateTime values. This is essential when working with data from systems that use UNIX timestamps to represent dates and times.

A Simple Solution:

A common approach involves using the DATEADD function:

<code class="language-sql">SELECT DATEADD(second, [unixtime], '19700101')
FROM [Table]</code>

Here, '19700101' represents the epoch—January 1, 1970, 00:00:00 UTC, the starting point for UNIX timestamps.

The Year 2038 Problem and its Solution:

The epoch time counts seconds since the epoch. SQL Server's DATEADD function, however, has an integer limit for the number of seconds. Adding more than 2,147,483,647 seconds results in an arithmetic overflow error. This is the "Year 2038 Problem."

To handle timestamps beyond 2038, a workaround is to divide the addition into two DATEADD operations:

<code class="language-sql">DECLARE @t BIGINT = 4147483645;
DECLARE @oneyear INT = 31622400; -- Approximate seconds in a year

SELECT DATEADD(second, @t % @oneyear, DATEADD(year, @t / @oneyear, '19700101'));</code>

This method first calculates the number of years and remaining seconds, then adds them sequentially, effectively overcoming the integer limitation and allowing conversion of timestamps far beyond the year 2038.

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