By default, MySQL uses the latin1 (cp1252 West European) character set and the latin1_swedish_ci collation that sorts according to Swedish/Finnish rules. These defaults are suitable for the United States and most of Western Europe.

All MySQL binary distributions are compiled with --with-extra-charsets=complex. This adds code to all standard programs that enables them to handle latin1 and all multi-byte character sets within the binary. Other character sets are loaded from a character-set definition file when needed.

The character set determines what characters are allowed in identifiers. The collation determines how strings are sorted by the ORDER BY and GROUP BY clauses of the SELECT statement.

You can change the default server character set and collation with the --character-set-server and --collation-server options when you start the server. The collation must be a legal collation for the default character set. (Use the SHOW COLLATION statement to determine which collations are available for each character set.) See Section 5.2.2, “Command Options”.

The character sets available depend on the --with-charset=charset_name and --with-extra-charsets=list-of-charsets | complex | all | none options to configure, and the character set configuration files listed in SHAREDIR/charsets/Index. See Section 2.4.14.2, “Typical configure Options”.

If you change the character set when running MySQL, that may also change the sort order. Consequently, you must run myisamchk -r -q --set-collation=collation_name on all MyISAM tables, or your indexes may not be ordered correctly.

When a client connects to a MySQL server, the server indicates to the client what the server's default character set is. The client switches to this character set for this connection.

You should use mysql_real_escape_string() when escaping strings for an SQL query. mysql_real_escape_string() is identical to the old mysql_escape_string() function, except that it takes the MYSQL connection handle as the first parameter so that the appropriate character set can be taken into account when escaping characters.

If the client is compiled with paths that differ from where the server is installed and the user who configured MySQL didn't include all character sets in the MySQL binary, you must tell the client where it can find the additional character sets it needs if the server runs with a different character set from the client. You can do this by specifying a --character-sets-dir option to indicate the path to the directory in which the dynamic MySQL character sets are stored. For example, you can put the following in an option file:

[client]
character-sets-dir=/usr/local/mysql/share/mysql/charsets

You can force the client to use specific character set as follows:

[client]
default-character-set=charset_name

This is normally unnecessary, however.

By default, mysqld produces error messages in English, but they can also be displayed in any of these other languages: Czech, Danish, Dutch, Estonian, French, German, Greek, Hungarian, Italian, Japanese, Korean, Norwegian, Norwegian-ny, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, or Swedish.

To start mysqld with a particular language for error messages, use the --language or -L option. The option value can be a language name or the full path to the error message file. For example:

shell> mysqld --language=swedish

Or:

shell> mysqld --language=/usr/local/share/swedish

The language name should be specified in lowercase.

By default, the language files are located in the share/LANGUAGE directory under the MySQL base directory.

You can also change the content of the error messages produced by the server. Details can be found in the MySQL Internals manual, available at http://forge.mysql.com/wiki/MySQL_Internals_Error_Messages. If you upgrade to a newer version of MySQL after changing the error messages, remember to repeat your changes after the upgrade.

This section discusses the procedure for adding a new character set to MySQL. You must have a MySQL source distribution to use these instructions. To choose the proper procedure, determine whether the character set is simple or complex:

For example, latin1 and danish are simple character sets, whereas big5 and czech are complex character sets.

In the following instructions, the name of the character set is represented by MYSET.

For a simple character set, do the following:

For a complex character set, do the following:

The sql/share/charsets/README file includes additional instructions.

If you want to have the character set included in the MySQL distribution, mail a patch to the MySQL internals mailing list. See Section 1.7.1, “MySQL Mailing Lists”.

to_lower[] and to_upper[] are simple arrays that hold the lowercase and uppercase characters corresponding to each member of the character set. For example:

to_lower['A'] should contain 'a'
to_upper['a'] should contain 'A'

sort_order[] is a map indicating how characters should be ordered for comparison and sorting purposes. Quite often (but not for all character sets) this is the same as to_upper[], which means that sorting is case-insensitive. MySQL sorts characters based on the values of sort_order[] elements. For more complicated sorting rules, see the discussion of string collating in Section 5.10.5, “String Collating Support”.

ctype[] is an array of bit values, with one element for one character. (Note that to_lower[], to_upper[], and sort_order[] are indexed by character value, but ctype[] is indexed by character value + 1. This is an old legacy convention for handling EOF.)

You can find the following bitmask definitions in m_ctype.h:

#define _U      01      /* Uppercase */
#define _L      02      /* Lowercase */
#define _N      04      /* Numeral (digit) */
#define _S      010     /* Spacing character */
#define _P      020     /* Punctuation */
#define _C      040     /* Control character */
#define _B      0100    /* Blank */
#define _X      0200    /* heXadecimal digit */

The ctype[] entry for each character should be the union of the applicable bitmask values that describe the character. For example, 'A' is an uppercase character (_U) as well as a hexadecimal digit (_X), so ctype['A'+1] should contain the value:

_U + _X = 01 + 0200 = 0201

If the sorting rules for your language are too complex to be handled with the simple sort_order[] table, you need to use the string collating functions.

The best documentation for this is the existing character sets. Look at the big5, czech, gbk, sjis, and tis160 character sets for examples.

You must specify the strxfrm_multiply_MYSET=N value in the special comment at the top of the file. N should be set to the maximum ratio the strings may grow during my_strxfrm_MYSET (it must be a positive integer).

If you want to add support for a new character set that includes multi-byte characters, you need to use the multi-byte character functions.

The best documentation for this is the existing character sets. Look at the euc_kr, gb2312, gbk, sjis, and ujis character sets for examples. These are implemented in the ctype-charset_name.c files in the strings directory.

You must specify the mbmaxlen_MYSET=N value in the special comment at the top of the source file. N should be set to the size in bytes of the largest character in the set.

If you try to use a character set that is not compiled into your binary, you might run into the following problems:

For MyISAM tables, you can check the character set name and number for a table with myisamchk -dvv tbl_name.

The MySQL server maintains several time zone settings:

The current session time zone setting affects display and storage of time values that are zone-sensitive. This includes the values displayed by functions such as NOW() or CURTIME(), and values stored in and retrieved from TIMESTAMP columns. Values for TIMESTAMP columns are converted from the current time zone to UTC for storage, and from UTC to the current time zone for retrieval. The current time zone setting does not affect values displayed by functions such as UTC_TIMESTAMP() or values in DATE, TIME, or DATETIME columns.

The current values of the global and client-specific time zones can be retrieved like this:

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

timezone values can be given in several formats, none of which are case sensitive:

The MySQL installation procedure creates the time zone tables in the mysql database, but does not load them. You must do so manually using the following instructions. (If you are upgrading to MySQL 4.1.3 or later from an earlier version, you can create the tables by upgrading your mysql database. Use the instructions in Section 5.5.8, “mysql_upgrade — Check Tables for MySQL Upgrade”. After creating the tables, you can load them.)

If your system has its own zoneinfo database (the set of files describing time zones), you should use the mysql_tzinfo_to_sql program for filling the time zone tables. Examples of such systems are Linux, FreeBSD, Sun Solaris, and Mac OS X. One likely location for these files is the /usr/share/zoneinfo directory. If your system does not have a zoneinfo database, you can use the downloadable package described later in this section.

The mysql_tzinfo_to_sql program is used to load the time zone tables. On the command line, pass the zoneinfo directory pathname to mysql_tzinfo_to_sql and send the output into the mysql program. For example:

shell> mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root mysql

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 to generate leap second information:

If your system is one that has no zoneinfo database (for example, Windows or HP-UX), you can use the package of pre-built time zone tables that is available for download at the MySQL Developer Zone:

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

This time zone package contains .frm, .MYD, and .MYI files for the MyISAM time zone tables. These tables should be part of the mysql database, so you should place the files in the mysql subdirectory of your MySQL server's data directory. The server should be stopped while you do this and restarted afterward.

Warning: Do not use the downloadable 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.

For information about time zone settings in replication setup, please see Section 6.7, “Replication Features and Known Problems”.

Staying Current with Time Zone Changes

As mentioned earlier, when the 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 two 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 one can be using named time zones, and you don't need to update the tables. 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, you should be sure to reload your time zone tables so that anyone who uses named time zones will get 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 these two queries:

SELECT CONVERT_TZ('2007-03-11 2:00:00','US/Eastern','US/Central');
SELECT CONVERT_TZ('2007-03-11 3:00:00','US/Eastern','US/Central');

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 would see an incorrect result like this:

mysql> SELECT CONVERT_TZ('2007-03-11 2:00:00','US/Eastern','US/Central');
+------------------------------------------------------------+
| CONVERT_TZ('2007-03-11 2:00:00','US/Eastern','US/Central') |
+------------------------------------------------------------+
| 2007-03-11 01:00:00                                        | 
+------------------------------------------------------------+

mysql> SELECT CONVERT_TZ('2007-03-11 3:00:00','US/Eastern','US/Central');
+------------------------------------------------------------+
| CONVERT_TZ('2007-03-11 3:00:00','US/Eastern','US/Central') |
+------------------------------------------------------------+
| 2007-03-11 02:00:00                                        |
+------------------------------------------------------------+

After updating the tables, you should see the correct result:

mysql> SELECT CONVERT_TZ('2007-03-11 2:00:00','US/Eastern','US/Central');
+------------------------------------------------------------+
| CONVERT_TZ('2007-03-11 2:00:00','US/Eastern','US/Central') |
+------------------------------------------------------------+
| 2007-03-11 01:00:00                                        | 
+------------------------------------------------------------+

mysql> SELECT CONVERT_TZ('2007-03-11 3:00:00','US/Eastern','US/Central');
+------------------------------------------------------------+
| CONVERT_TZ('2007-03-11 3:00:00','US/Eastern','US/Central') |
+------------------------------------------------------------+
| 2007-03-11 01:00:00                                        | 
+------------------------------------------------------------+

Beginning with MySQL 5.0.25, the locale indicated by the lc_time_names system variable controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions.

Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting, but any client can examine or set its lc_time_names value as shown in the following example:

mysql> SET NAMES 'utf8';
Query OK, 0 rows affected (0.09 sec)

mysql> SELECT @@lc_time_names;
+-----------------+
| @@lc_time_names |
+-----------------+
| en_US           | 
+-----------------+
1 row in set (0.00 sec)

mysql> SELECT DAYNAME('2010-01-01'), MONTHNAME('2010-01-01');
+-----------------------+-------------------------+
| DAYNAME('2010-01-01') | MONTHNAME('2010-01-01') |
+-----------------------+-------------------------+
| Friday                | January                 | 
+-----------------------+-------------------------+
1 row in set (0.00 sec)

mysql> SELECT DATE_FORMAT('2010-01-01','%W %a %M %b');
+-----------------------------------------+
| DATE_FORMAT('2010-01-01','%W %a %M %b') |
+-----------------------------------------+
| Friday Fri January Jan                  | 
+-----------------------------------------+
1 row in set (0.00 sec)

mysql> SET lc_time_names = 'es_MX';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @@lc_time_names;
+-----------------+
| @@lc_time_names |
+-----------------+
| es_MX           | 
+-----------------+
1 row in set (0.00 sec)

mysql> SELECT DAYNAME('2010-01-01'), MONTHNAME('2010-01-01');
+-----------------------+-------------------------+
| DAYNAME('2010-01-01') | MONTHNAME('2010-01-01') |
+-----------------------+-------------------------+
| viernes               | enero                   | 
+-----------------------+-------------------------+
1 row in set (0.00 sec)

mysql> SELECT DATE_FORMAT('2010-01-01','%W %a %M %b');
+-----------------------------------------+
| DATE_FORMAT('2010-01-01','%W %a %M %b') |
+-----------------------------------------+
| viernes vie enero ene                   | 
+-----------------------------------------+
1 row in set (0.00 sec)

The day or month name for each of the affected functions is converted from utf8 to the character set indicated by the character_set_connection system variable.

lc_time_names may be set to any of the following locale values:

lc_time_names currently does not affect the STR_TO_DATE() or GET_FORMAT() function.