How Do MySQL Time Zone Settings Affect Date and Time Display and Storage?

How MySQL Time Zone Settings Influence Date and Time Representations

When dealing with date and time data in MySQL, it's crucial to understand how time zones affect their values. The time zone settings in MySQL influence how dates and times are stored and displayed within the database system.

MySQL provides three levels at which time zones can be configured:

1. [mysqld] Section in "my.cnf"

   By default, the time zone specified in the "[mysqld]" section of the "my.cnf" configuration file determines the global time zone.

2. @@global.time_zone Variable

   This variable sets the global time zone for all database connections. Its value can be modified using the "SET GLOBAL time_zone" command.

3. @@session.time_zone Variable

   This variable sets the time zone for the current user session. It can be modified using the "SET time_zone" command.

To check the current value of a time zone variable, use the "SELECT @@variable_name" syntax.

It's important to be aware that the stored date and time values remain unchanged when the time zone changes. However, existing timestamp columns will display different datetime values since they are internally stored as UTC timestamps and displayed externally using the current MySQL time zone.

For example, you may observe discrepancies in time displays between two different servers with different time zone configurations. This behavior is due to the impact of time zone settings on the interpretation of datetime values.

To ensure consistent and accurate handling of date and time data across different time zones, it's advisable to set the MySQL time zone to UTC for convenience and compatibility.

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