How Does MySQL\'s CONVERT_TZ() Function Handle Time Zones and Daylight Saving Time?

MySQL CONVERT_TZ() Time Zone Handling

Question 1: Daylight Saving Time Consideration

Yes, you are correct. By specifying the time zone name (e.g., "US/Eastern"), CONVERT_TZ() does take daylight saving time into account. Calling CONVERT_TZ('00:00:00', 'UTC', 'US/EASTERN') returns '19:00:00' in January, recognizing that Eastern Time is behind UTC by 5 hours. During daylight saving time, the result would be '20:00:00' as Eastern Time moves an hour ahead.

Question 2: Time Zone Table Update

If you rely solely on the time zone name, you do not need to constantly update the time zone table to keep the offsets up to date. CONVERT_TZ() considers the current time zone settings and daylight saving time rules.

Question 3: Troubleshooting NULL Returns

The NULL return in your sample query (CONVERT_TZ('2004-01-01 12:00:00','GMT','MET')) could indeed be caused by missing time zone tables. To verify this, run the following query:

SELECT CONVERT_TZ(now(),'US/Eastern','US/Central');

If this also returns NULL, it indicates that the time zone tables have not been set up properly.

Additional Tips

• For web applications, you can use JavaScript to obtain the user's time zone.

• Instead of adding or subtracting time directly, you can use the INTERVAL keyword in MySQL to handle time calculations. For example, you could subtract one day and add four hours by using:

  now() - interval 1 day + interval 4 hour

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