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

MySQL CONVERT_TZ() with Daylight Saving Time

When storing daily alerts in a database that are specified in user-defined local time zones, it is crucial to consider daylight saving time (DST). This article explores the use of the CONVERT_TZ() function to accommodate DST and addresses common questions related to its implementation.

Question 1: Time Zone Conversion with DST

The CONVERT_TZ() function takes into account DST when specifying time zone names. For instance, converting UTC time to US/Eastern time should yield different results depending on whether DST is in effect or not. This aligns with your understanding that CONVERT_TZ('00:00:00', 'UTC', 'US/EASTERN') should return '19:00:00' on January 1 and '20:00:00' on July 1.

Question 2: MySQL Time Zone Table Updates

If the CONVERT_TZ() function is working correctly, there is generally no need to manually update MySQL's time zone table. MySQL maintains an internal database that stores time zone information and updates it as necessary based on changes in time zone regulations. However, if you have made customizations to your time zone settings, it is recommended to periodically review the table to ensure accuracy.

Question 3: Null Values from CONVERT_TZ()

If CONVERT_TZ() returns NULL, this indicates that the MySQL time zone tables are not set up properly. You can check this by running the following query:

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

If this query returns NULL, it suggests that the tables are not configured. To resolve this issue, you can refer to the MySQL documentation for instructions on setting up time zone tables.

Alternative Approach

If you do not want to rely on the MySQL time zone tables, you can use the following approach:

1. Store the user's time zone offset from UTC in hours in a separate table.
2. Use the utc_timezone() function to get the current UTC time.
3. Calculate the user's local time by subtracting the time zone offset.

For example:

SELECT utc_timezone() - interval user_timezone_offset_in_hours hour
FROM userinfo a
WHERE user_id = 999;

The above is the detailed content of How Does MySQL\'s CONVERT_TZ() Function Handle Daylight Saving Time?. For more information, please follow other related articles on the PHP Chinese website!