This section describes the time zone settings maintained by MySQL, how to load the system tables required for named time support, how to stay current with time zone changes, and how to enable leap-second support.
For information about time zone settings in replication setups, please see Section 17.4.1, “Replication Features and Issues”.
MySQL Server maintains several time zone settings:
The system time zone. When the server starts, it attempts to determine the time zone of the host machine automatically and uses it to set the
system_time_zonesystem variable. The value does not change thereafter.
To explicitly specify the system time zone for MySQL Server at startup, set the
TZenvironment variable before you start mysqld. If you start the server using mysqld_safe, its
--timezoneoption provides another way to set the system time zone. The permissible values for
--timezoneare system dependent. Consult your operating system documentation to see what values are acceptable.
The server current time zone. The global
time_zonesystem variable indicates the time zone the server currently is operating in. The initial
'SYSTEM', which indicates that the server time zone is the same as the system time zone.Note
If set to
SYSTEM, every MySQL function call that requires a time zone calculation makes a system library call to determine the current system time zone. This call may be protected by a global mutex, resulting in contention.
The initial global server time zone value can be specified explicitly at startup with the
--default-time-zoneoption on the command line, or you can use the following line in an option file:
If you have the
SUPERprivilege, you can set the global server time zone value at runtime with this statement:
SET GLOBAL time_zone = timezone;
Per-session time zones. Each client that connects has its own session time zone setting, given by the session
time_zonevariable. Initially, the session variable takes its value from the global
time_zonevariable, but the client can change its own time zone with this statement:
SET time_zone = timezone;
The session time zone setting affects display and storage of
time values that are zone-sensitive. This includes the values
displayed by functions such as
CURTIME(), and values stored in
and retrieved from
columns. Values for
columns are converted from the session time zone to UTC for
storage, and from UTC to the session time zone for retrieval.
The session time zone setting does not affect values displayed
by functions such as
UTC_TIMESTAMP() or values in
DATETIME columns. Nor are values
in those data types stored in UTC; the time zone applies for
them only when converting from
TIMESTAMP values. If you want
locale-specific arithmetic for
DATETIME values, convert them to
UTC, perform the arithmetic, and then convert back.
The current global and session time zone values can be retrieved like this:
SELECT @@GLOBAL.time_zone, @@SESSION.time_zone;
timezone values can be given in
several formats, none of which are case sensitive:
As the value
'SYSTEM', indicating that the server time zone is the same as the system time zone.
As a string indicating an offset from UTC, such as
As a named time zone, such as
'MET'. Named time zones can be used only if the time zone information tables in the
mysqldatabase have been created and populated.
Several tables in the
mysql system database
exist to store time zone information (see
Section 5.3, “The mysql System Database”). The MySQL installation
procedure creates the time zone tables, but does not load them.
To do so manually, use the following instructions.
Loading the time zone information is not necessarily a one-time operation because the information changes occasionally. When such changes occur, applications that use the old rules become out of date and you may find it necessary to reload the time zone tables to keep the information used by your MySQL server current. See Staying Current with Time Zone Changes.
If your system has its own
zoneinfo database (the set
of files describing time zones), use the
mysql_tzinfo_to_sql program to load the time
zone tables. Examples of such systems are Linux, macOS, FreeBSD,
and Solaris. One likely location for these files is the
/usr/share/zoneinfo directory. If your
system has no zoneinfo database, you can use a downloadable
package, as described later in this section.
mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root -p mysql
The mysql command shown here assumes that you
connect to the server using an account such as
root that has privileges for modifying tables
mysql system database. Adjust the
connection parameters as required.
mysql_tzinfo_to_sql also can be used to load a single time zone file or generate leap second information:
To load a single time zone file
tz_filethat corresponds to a time zone name
tz_name, invoke mysql_tzinfo_to_sql like this:
mysql_tzinfo_to_sql tz_file tz_name | mysql -u root -p mysql
With this approach, you must execute a separate command to load the time zone file for each named zone that the server needs to know about.
If your time zone must account for leap seconds, initialize leap second information like this, where
tz_fileis the name of your time zone file:
mysql_tzinfo_to_sql --leap tz_file | mysql -u root -p mysql
After running mysql_tzinfo_to_sql, restart the server so that it does not continue to use any previously cached time zone data.
If your system has no zoneinfo database (for example, Windows), you can use a package that is available for download at the MySQL Developer Zone:
Do not use a downloadable time zone package if your system has a zoneinfo database. Use the mysql_tzinfo_to_sql utility instead. Otherwise, you may cause a difference in datetime handling between MySQL and other applications on your system.
You can use either a package that contains SQL statements to
populate your existing time zone tables, or a package that
MyISAM time zone tables to
replace your existing tables:
To use a time zone package that contains SQL statements, download and unpack it, then load the unpacked file contents into your existing time zone tables:
mysql -u root -p mysql < file_name
Then restart the server.
To use a time zone package that contains
.MYIfiles for the
MyISAMtime zone tables, download and unpack it. These table files are part of the
mysqldatabase, so you should place the files in the
mysqlsubdirectory of your MySQL server's data directory. Stop the server before doing this and restart it afterward.
When time zone rules change, applications that use the old rules become out of date. To stay current, it is necessary to make sure that your system uses current time zone information is used. For MySQL, there are multiple factors to consider in staying current:
The operating system time affects the value that the MySQL server uses for times if its time zone is set to
SYSTEM. Make sure that your operating system is using the latest time zone information. For most operating systems, the latest update or service pack prepares your system for the time changes. Check the website for your operating system vendor for an update that addresses the time changes.
If you replace the system's
/etc/localtimetime zone file with a version that uses rules differing from those in effect at mysqld startup, restart mysqld so that it uses the updated rules. Otherwise, mysqld might not notice when the system changes its time.
If you use named time zones with MySQL, make sure that the time zone tables in the
mysqldatabase are up to date:
If your system has its own zoneinfo database, reload the MySQL time zone tables whenever the zoneinfo database is updated.
For systems that do not have their own zoneinfo database, check the MySQL Developer Zone for updates. When a new update is available, download it and use it to replace the content of your current time zone tables.
For instructions for both methods, see Populating the Time Zone Tables. mysqld caches time zone information that it looks up, so after updating the time zone tables, restart mysqld to make sure that it does not continue to serve outdated time zone data.
If you are uncertain whether named time zones are available, for use either as the server's time zone setting or by clients that set their own time zone, check whether your time zone tables are empty. The following query determines whether the table that contains time zone names has any rows:
mysql> SELECT COUNT(*) FROM mysql.time_zone_name; +----------+ | COUNT(*) | +----------+ | 0 | +----------+
A count of zero indicates that the table is empty. In this case, no applications currently are using named time zones, and you need not update the tables (unless you want to enable named time zone support). A count greater than zero indicates that the table is not empty and that its contents are available to be used for named time zone support. In this case, be sure to reload your time zone tables so that applications that use named time zones will obtain correct query results.
To check whether your MySQL installation is updated properly for a change in Daylight Saving Time rules, use a test like the one following. The example uses values that are appropriate for the 2007 DST 1-hour change that occurs in the United States on March 11 at 2 a.m.
The test uses this query:
SELECT CONVERT_TZ('2007-03-11 2:00:00','US/Eastern','US/Central') AS time1, CONVERT_TZ('2007-03-11 3:00:00','US/Eastern','US/Central') AS time2;
The two time values indicate the times at which the DST change occurs, and the use of named time zones requires that the time zone tables be used. The desired result is that both queries return the same result (the input time, converted to the equivalent value in the 'US/Central' time zone).
Before updating the time zone tables, you see an incorrect result like this:
+---------------------+---------------------+ | time1 | time2 | +---------------------+---------------------+ | 2007-03-11 01:00:00 | 2007-03-11 02:00:00 | +---------------------+---------------------+
After updating the tables, you should see the correct result:
+---------------------+---------------------+ | time1 | time2 | +---------------------+---------------------+ | 2007-03-11 01:00:00 | 2007-03-11 01:00:00 | +---------------------+---------------------+
Leap second values are returned with a time part that ends with
:59:59. This means that a function such as
NOW() can return the same value
for two or three consecutive seconds during the leap second. It
remains true that literal temporal values having a time part
that ends with
:59:61 are considered invalid.
If it is necessary to search for
TIMESTAMP values one second
before the leap second, anomalous results may be obtained if you
use a comparison with
values. The following example demonstrates this. It changes the
session time zone to UTC so there is no difference between
TIMESTAMP values (which
are in UTC) and displayed values (which have time zone
mysql> CREATE TABLE t1 ( a INT, ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (ts) ); Query OK, 0 rows affected (0.01 sec) mysql> -- change to UTC mysql> SET time_zone = '+00:00'; Query OK, 0 rows affected (0.00 sec) mysql> -- Simulate NOW() = '2008-12-31 23:59:59' mysql> SET timestamp = 1230767999; Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO t1 (a) VALUES (1); Query OK, 1 row affected (0.00 sec) mysql> -- Simulate NOW() = '2008-12-31 23:59:60' mysql> SET timestamp = 1230768000; Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO t1 (a) VALUES (2); Query OK, 1 row affected (0.00 sec) mysql> -- values differ internally but display the same mysql> SELECT a, ts, UNIX_TIMESTAMP(ts) FROM t1; +------+---------------------+--------------------+ | a | ts | UNIX_TIMESTAMP(ts) | +------+---------------------+--------------------+ | 1 | 2008-12-31 23:59:59 | 1230767999 | | 2 | 2008-12-31 23:59:59 | 1230768000 | +------+---------------------+--------------------+ 2 rows in set (0.00 sec) mysql> -- only the non-leap value matches mysql> SELECT * FROM t1 WHERE ts = '2008-12-31 23:59:59'; +------+---------------------+ | a | ts | +------+---------------------+ | 1 | 2008-12-31 23:59:59 | +------+---------------------+ 1 row in set (0.00 sec) mysql> -- the leap value with seconds=60 is invalid mysql> SELECT * FROM t1 WHERE ts = '2008-12-31 23:59:60'; Empty set, 2 warnings (0.00 sec)
To work around this, you can use a comparison based on the UTC value actually stored in the column, which has the leap second correction applied:
mysql> -- selecting using UNIX_TIMESTAMP value return leap value mysql> SELECT * FROM t1 WHERE UNIX_TIMESTAMP(ts) = 1230768000; +------+---------------------+ | a | ts | +------+---------------------+ | 2 | 2008-12-31 23:59:59 | +------+---------------------+ 1 row in set (0.00 sec)