How Can MySQL Datetime Fields Handle Daylight Saving Time Accurately?

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

When working with datetime fields in MySQL, it is crucial to consider the impact of daylight savings time (DST). As the case study illustrates, the transition from standard time to DST can lead to ambiguous time representations, especially when storing data in a timezone that observes DST.

2009-11-01 01:30:00 -04:00 vs. 2009-11-01 01:30:00 -05:00

The Problem

Both DATETIME and TIMESTAMP field types present challenges in accurately handling data in DST-observing timezones. DATETIME fields do not handle DST internally, while TIMESTAMP fields automatically convert data to and from UTC, assuming it is in the system's local timezone, which can lead to data loss during the round-trip conversion if DST is a factor.

The Solution

To address this issue, it is recommended to store datetime data in a non-DST timezone, such as UTC. This allows you to control the conversion logic outside of MySQL and explicitly store the intended UTC equivalent of the local time you wish to represent.

Data Retrieval

When retrieving data from the database, ensure you interpret it as UTC outside of MySQL using functions like strtotime() or PHP's DateTime class. This provides an accurate Unix timestamp, avoiding ambiguity.

Data Storage

Prior to storing data in the database, convert it to the desired UTC time externally using PHP's DateTime class or similar mechanisms. Specify the local time and timezone explicitly to ensure the correct UTC representation is saved to the DATETIME field.

Key Considerations

Remember that MySQL's date/time math functions may not work correctly around DST boundaries if data is stored in a DST timezone. Therefore, storing data in UTC is essential for reliable calculations.

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