How to Handle Daylight Savings Time with MySQL `DATETIME` Fields?

MySQL Datetime Fields and Daylight Savings Time: Handling the "Extra" Hour

This discussion addresses the challenges faced when dealing with MySQL datetime fields in the context of daylight savings time (DST). The ambiguity that arises during the transition period can lead to confusion and incorrect data storage.

The Problem

During the DST transition, an hour is "gained" or "lost." This transition point creates two instances of the same time, such as 01:30:00 occurring once with an offset of -04:00 and again with an offset of -05:00. This ambiguity makes it unclear which instance of 01:30:00 is being referenced.

Limitations of Datetime and Timestamp Fields

Contrary to previous assumptions, DATETIME and TIMESTAMP field types behave differently in the presence of DST. While TIMESTAMP fields convert data to UTC before storage, DATETIME fields store data directly without conversion. However, both field types cannot accurately store data in timezones affected by DST.

The Solution

To overcome these limitations, it is necessary to store data in a non-DST timezone, such as UTC. This can be achieved by converting data from the system timezone to UTC before saving it to the DATETIME field.

Additional Considerations

• MySQL's date/time math functions may not work reliably around DST boundaries if data is stored in a DST timezone.
• All time calculations should be performed outside of MySQL using a compatible programming language, such as PHP or Python.
• When retrieving data from the database, interpret it as UTC outside of MySQL to obtain an accurate Unix timestamp.

By implementing these strategies, it is possible to accurately handle datetime data in MySQL even in the presence of daylight savings time.

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