How Can I Determine MySQL's Actual Time Zone Setting When @@global.time_zone Returns 'SYSTEM'?

Obtaining MySQL's Current Time Zone Setting

Determining the time zone setting of a MySQL server has sparked some confusion among users. Contrary to initial assumptions, the @@global.time_zone and @@session.time_zone variables often return "SYSTEM" as the time zone. However, if MySQL is configured to utilize the system's time zone, this response provides little insight.

Retrieving the Time Zone Information

According to the MySQL manual, the following command can be used to retrieve the current global and client-specific time zones:

mysql> SELECT @@global.time_zone, @@session.time_zone;

Handling the "SYSTEM" Response

If MySQL returns "SYSTEM" as the time zone, PHP developers can obtain the actual time zone used by the system using date_default_timezone_get. However, it's important to note that PHP may run on a different server than the MySQL database, so this assumption might not always hold true.

Consideration for Stored Date and Time Values

It's crucial to remember that date and time values in MySQL do not include time zone information. Therefore, the server's time zone setting only affects functions that retrieve the current time, such as now() or unix_timestamp(). It doesn't influence the storage or interpretation of existing data in the database.

Importance of Storing Time Zone Information

To ensure accurate handling of date and time data, it's recommended to store values in GMT (which does not observe Daylight Savings Time) and convert them to the desired time zone as needed. This approach eliminates potential ambiguities arising from server configuration or Daylight Savings Time transitions.

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