Time Zones in PHP and MySQL

Integrating a time zone system into PHP applications can be challenging, but it's essential when handling data from different time zones. Here's a comprehensive guide to address the most common concerns and provide practical solutions.

Storing Datetimes in MySQL

• Use DATETIME or TIMESTAMP: DATETIME provides more precision, while TIMESTAMP is suitable when accuracy down to the second isn't crucial.
• Store in UTC: Set your MySQL connection timezone to UTC to ensure all datetimes are handled consistently.

Converting Datetimes

• To MySQL: Convert PHP datetimes to UTC before storing in MySQL using DateTime::setTimezone('UTC').
• From MySQL: Create a PHP DateTime object from MySQL values, and specify a UTC timezone to ensure correct interpretation.

Handling Daylight Savings Time (DST)

MySQL doesn't handle DST natively. PHP's DateTimeZone class provides named time zones that automatically handle DST based on the user's location, which should be used for user-facing timestamps.

Legacy Data Migration

If existing data was inserted without considering time zones, use MySQL's CONVERT_TZ function to correct the timestamps during selects and updates. Alternatively, update the timestamps by converting to UTC and then back to the local time zone.

Selecting Time Zones for User Preference

• Offer Named Time Zones: Use DateTimeZone::listIdentifiers() to retrieve a list of named time zones.
• Store in Database: Save the user's selected time zone as a key or identifier in the database.

Example Code

Note: It's important to store and convert timestamps consistently to avoid data inconsistencies and user confusion. By following these guidelines, you can effectively manage time zones in your PHP and MySQL applications.