How Can I Avoid Ambiguous Time References in MySQL DATETIME Fields During Daylight Saving Time?

Ambiguous Time References with MySQL DATETIME and Daylight Savings Time

In time zones that observe Daylight Savings Time (DST), referencing a specific time during the hour change can be ambiguous. For instance, "1:30am" in America/New York could refer to either 01:30:00 -04:00 or 01:30:00 -05:00. This ambiguity arises when storing times in MySQL DATETIME fields.

The Behavior of DATETIME and TIMESTAMP

MySQL DATETIME fields store time values as they are received, without regard to the timezone information. TIMESTAMP fields, on the other hand, convert the provided value to UTC time based on the server's timezone. This behavior can lead to inaccuracies when managing times that overlap with DST transitions.

Solutions for Accurate Time Management

To resolve this issue, it is recommended to store date and time information in a non-DST timezone, such as UTC. This ensures consistent interpretation regardless of the server's timezone or DST status.

Converting to UTC Before Storing

When storing data in a DATETIME field, convert the time from the system timezone to UTC using external scripting logic. For example, with PHP's DateTime class, you can explicitly specify a non-DST timezone and then convert it to UTC before saving.

Additional Considerations

MySQL date/time math functions may not work reliably within DST boundaries if the data is stored in a DST timezone. Therefore, it is recommended to handle date/time calculations using external scripts instead.

Conclusion

By understanding the nuanced behavior of DATETIME and TIMESTAMP fields in MySQL and employing the recommended strategies for time conversion and storage, you can effectively manage ambiguous times during DST transitions, ensuring accurate and consistent time management in your MySQL database.

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