Does MySQL\'s CONVERT_TZ() Function Handle Daylight Saving Time, and How Can I Troubleshoot Time Zone Issues?

MySQL CONVERT_TZ() with Daylight Saving Time Considerations

Question 1:

Yes, your understanding is correct. CONVERT_TZ() takes daylight saving time into account when specifying the time zone name. For example, CONVERT_TZ('00:00:00', 'UTC', 'US/EASTERN') would indeed return '19:00:00' on January 1 and '20:00:00' on July 1.

Question 2:

No, you do not need to constantly update MySQL's time zone table to keep the time zone UTC offsets up to date. MySQL automatically updates the table as time zone rules change.

Question 3:

The result of SELECT CONVERT_TZ('2004-01-01 12:00:00','GMT','MET') yielding "NULL" could indicate that the time zone tables are not set up properly.

To check this, you can run the following query:

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

If the result is not NULL, then the time zone tables are set up correctly.

Alternative Time Zone Offset Calculation:

If you do not have the time zone tables set up, you can still calculate the time zone offset using the following query:

select utc_timezone() - interval user_timezone_offset_in_hours hour
from userinfo a
where user_id = 999;

However, this approach requires you to manually update the user's time zone offset.

Getting Time Zone via JavaScript:

For web applications, you can obtain the user's time zone via JavaScript. The following link provides an example of how to do this:

[JavaScript Time Zone Detection](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl.DateTimeFormat)

Using INTERVAL for Time Calculations:

The INTERVAL keyword allows for convenient addition and subtraction of time values. For example, the following query subtracts 1 day, 4 hours, and 8 minutes from the current time:

select now() a, now() - interval 1 day + interval 4 hour + interval 8 minute b;

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