How to Convert a Bigint UNIX Timestamp to DateTime in SQL Server?

SQL Server: Transforming Bigint UNIX Timestamps into DateTime Values

This guide details the conversion of bigint UNIX timestamps to DateTime objects within SQL Server. The process necessitates a formula to account for the temporal disparity between the UNIX and SQL Server epochs.

The Conversion Method:

The following SQL statement effectively performs the conversion:

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

Understanding the Formula:

• '19700101': This represents the UNIX epoch—the starting point for UNIX timestamps (January 1st, 1970, 00:00:00 UTC).
• DATEADD(second, [unixtime], '19700101'): The DATEADD function adds the number of seconds specified by [unixtime] (your bigint timestamp) to the UNIX epoch, yielding the corresponding DateTime value.

Epoch Time Explained:

Epoch time signifies the number of seconds elapsed since the UNIX epoch.

Addressing the Year 2038 Issue:

SQL Server's DATEADD function utilizes an integer argument for the number of seconds. Timestamps exceeding 2,147,483,647 seconds (roughly 68 years) will result in an arithmetic overflow error.

Resolving the Year 2038 Limitation:

To overcome this, divide the timestamp into years and remaining seconds, using two separate DATEADD operations. This extended approach handles timestamps beyond the year 2038. (A specific example of this multi-step approach would need to be added here if desired, showing the breakdown into years and remaining seconds.)

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