How Can MySQL DATETIME Fields Accurately Handle Daylight Savings Time Ambiguity?

MySQL Datetime Fields and Daylight Savings Time: Handling Ambiguous Hours

MySQL datetime fields present a unique challenge when dealing with daylight savings time transitions, where one hour appears twice in a day due to the time shift. This ambiguity arises because datetime fields store timestamps without explicitly specifying time zone offsets.

The Problem:

Consider the following scenario in the America/New York timezone:

• 01:59:00 -04:00
• 01:00:00 -05:00 (after time shift)

Saving "1:30am" to a MySQL database without specifying an offset results in ambiguity:

• "2009-11-01 00:30:00" is stored as 2009-11-01 00:30:00 -04:00
• "2009-11-01 01:30:00" is stored as 2009-11-01 01:30:00 -05:00

This poses a challenge in determining which 1:30am is being referenced.

The Solution: Understanding DATETIME and TIMESTAMP

Contrary to popular belief, DATETIME and TIMESTAMP fields behave differently in MySQL:

• TIMESTAMP: Converted to UTC time upon insertion and back to local time upon retrieval.
• DATETIME: Stored directly without any timezone conversion.

Best Practice: Using DATETIME Fields with UTC

To accurately store timestamps during daylight savings time transitions, it is recommended to use DATETIME fields and specify the UTC timezone explicitly. This allows you to convert timestamps to UTC before saving and ensures they are interpreted correctly upon retrieval.

Steps to Implement:

1. When Retrieving Data:

   • Interpret the data as UTC using PHP's strtotime() or DateTime class to get an accurate Unix timestamp.

2. When Storing Data:

   • Convert the timestamp to UTC (e.g., using PHP's DateTime class) and save it to a DATETIME field.

By following these steps, you can accurately handle ambiguous timestamps during daylight savings time transitions and ensure the integrity of your data.

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