How to Convert UNIX Timestamps to DateTime in SQL Server, Handling the Year 2038 Problem?

SQL Server: Converting UNIX Timestamps to DateTime

This guide explains how to efficiently convert UNIX timestamps (stored as bigint) into the DateTime data type within SQL Server, specifically addressing the potential "Year 2038 Problem."

Standard Conversion

A straightforward method uses the DATEADD function:

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

This leverages the Unix epoch ('1970-01-01 00:00:00 UTC') as the starting point for the timestamp calculation.

Addressing the Year 2038 Problem

The DATEADD function's second parameter is an int, limiting its capacity. To handle timestamps exceeding the int limit (the Year 2038 problem), we need a more robust approach.

Solution: Modular Arithmetic for Large Timestamps

The solution involves splitting the addition into years and remaining seconds using modular arithmetic:

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

SELECT (@t / @oneyear) AS YearsToAdd;  -- Number of years
SELECT (@t % @oneyear) AS RemainingSeconds; -- Remaining seconds

-- Calculate the DateTime
SELECT DATEADD(SECOND, @t % @oneyear, DATEADD(YEAR, @t / @oneyear, '19700101'));</code>

This method correctly handles timestamps far beyond the year 2038 by first adding the years and then the remaining seconds. This avoids integer overflow errors.

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