How Can MySQL Handle Ambiguous Datetimes During Daylight Saving Time Transitions?

Handling Ambiguous Datetimes with Daylight Savings Time in MySQL

When daylight savings time (DST) occurs, there is an ambiguous hour where it's difficult to determine the intended time reference. For instance, in the America/New York timezone, 1:30am can occur twice during the fall transition period.

Problem:

MySQL's DATETIME and TIMESTAMP fields present unique challenges when it comes to handling these ambiguous times. DATETIME fields store dates and times as is, without considering time zones or DST conversions. TIMESTAMP fields convert input timestamps to UTC and vice versa.

Solution:

1. Use DATETIME Fields:

Convert timestamps to UTC before storing them in DATETIME fields. This ensures that you have control over the exact UTC time to save.

2. Interpretation of Retrieved Data:

Interpret timestamps retrieved from DATETIME fields as UTC timestamps outside of MySQL. This prevents ambiguities introduced by MySQL's date/time functions.

3. Avoid TIMESTAMP Fields:

Avoid using TIMESTAMP fields as they can lead to inconsistent conversions between local time and UTC when DST is involved.

Implementation:

Retrieving Data:

// Example using PHP's DateTime class
$timestamp = strtotime($db_timestamp . ' UTC');

Storing Data:

// Example using PHP's DateTime class
$UTCDateTime = new DateTime('2009-11-01 1:30:00 EST');
$db_timestamp = $UTCDateTime->format('Y-m-d H:i:s');

Considerations:

• MySQL's date/time functions can't handle DST boundaries reliably when storing data in DST timezones.
• Specify the offset in DATETIME fields is ignored by MySQL.

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