7.1.15 MySQL Server Time Zone Support (original) (raw)

7.1.15 MySQL Server Time Zone Support

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.

Beginning with MySQL 8.0.19, time zone offsets are also supported for inserted datetime values; see Section 13.2.2, “The DATE, DATETIME, and TIMESTAMP Types”, for more information.

For information about time zone settings in replication setups, see Section 19.5.1.14, “Replication and System Functions” andSection 19.5.1.33, “Replication and Time Zones”.

Time Zone Variables

MySQL Server maintains several time zone settings:

default-time-zone='timezone'

If you have theSYSTEM_VARIABLES_ADMIN privilege (or the deprecatedSUPER privilege), you can set the global server time zone value at runtime with this statement: 

SET GLOBAL time_zone = timezone;  
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 asNOW() orCURTIME(), and values stored in and retrieved from TIMESTAMP columns. Values for TIMESTAMP 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 asUTC_TIMESTAMP() or values inDATE,TIME, orDATETIME columns. Nor are values in those data types stored in UTC; the time zone applies for them only when converting fromTIMESTAMP values. If you want locale-specific arithmetic forDATE,TIME, orDATETIME 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:

mysql> SET time_zone = 'UTC';  
ERROR 1298 (HY000): Unknown or incorrect time zone: 'UTC'

Populating the Time Zone Tables

Several tables in the mysql system schema exist to store time zone information (seeSection 7.3, “The mysql System Schema”). The MySQL installation procedure creates the time zone tables, but does not load them. To do so manually, use the following instructions.

Note

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. SeeStaying Current with Time Zone Changes.

If your system has its ownzoneinfo database (the set of files describing time zones), use themysql_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.

To load the time zone tables from the command line, pass the zoneinfo directory path name tomysql_tzinfo_to_sql and send the output into the mysql program. For example:

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 asroot that has privileges for modifying tables in the mysql system schema. Adjust the connection parameters as required.

mysql_tzinfo_to_sql reads your system's time zone files and generates SQL statements from them.mysql processes those statements to load the time zone tables.

mysql_tzinfo_to_sql also can be used to load a single time zone file or generate leap second information:

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.

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 containing SQL statements that is available for download at the MySQL Developer Zone:

https://dev.mysql.com/downloads/timezones.html

Warning

Do not use a downloadable time zone package if your system has a zoneinfo database. Use themysql_tzinfo_to_sql utility instead. Otherwise, you may cause a difference in datetime handling between MySQL and other applications on your system.

To use an SQL-statement time zone package that you have downloaded, unpack it, then load the unpacked file contents into the time zone tables:

mysql -u root -p mysql < file_name

Then restart the server.

Warning

Do not use a downloadable time zone package that contains MyISAM tables. That is intended for older MySQL versions. MySQL now usesInnoDB for the time zone tables. Trying to replace them with MyISAM tables causes problems.

Staying Current with Time Zone Changes

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:

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 can 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 |
+---------------------+---------------------+

Time Zone Leap Second Support

Leap second values are returned with a time part that ends with:59:59. This means that a function such asNOW() 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 :59:60 or:59:61 are considered invalid.

If it is necessary to search forTIMESTAMP values one second before the leap second, anomalous results may be obtained if you use a comparison with '_`YYYY-MM-DD hh:mm:ss`_' values. The following example demonstrates this. It changes the session time zone to UTC so there is no difference between internalTIMESTAMP values (which are in UTC) and displayed values (which have time zone correction applied).

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)