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10.5 Configuring Application Character Set and Collation

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For applications that store data using the default MySQL character set and collation (utf8mb4, utf8mb4_0900_ai_ci), no special configuration should be needed. If applications require data storage using a different character set or collation, you can configure character set information several ways:

  • Specify character settings per database. For example, applications that use one database might use the default of utf8mb4, whereas applications that use another database might use sjis.

  • Specify character settings at server startup. This causes the server to use the given settings for all applications that do not make other arrangements.

  • Specify character settings at configuration time, if you build MySQL from source. This causes the server to use the given settings as the defaults for all applications, without having to specify them at server startup.

When different applications require different character settings, the per-database technique provides a good deal of flexibility. If most or all applications use the same character set, specifying character settings at server startup or configuration time may be most convenient.

For the per-database or server-startup techniques, the settings control the character set for data storage. Applications must also tell the server which character set to use for client/server communications, as described in the following instructions.

The examples shown here assume use of the latin1 character set and latin1_swedish_ci collation in particular contexts as an alternative to the defaults of utf8mb4 and utf8mb4_0900_ai_ci.

  • Specify character settings per database.  To create a database such that its tables will use a given default character set and collation for data storage, use a CREATE DATABASE statement like this:

    1. CREATE DATABASE mydb
    2.   CHARACTER SET latin1
    3.   COLLATE latin1_swedish_ci;

    Tables created in the database will use latin1 and latin1_swedish_ci by default for any character columns.

    Applications that use the database should also configure their connection to the server each time they connect. This can be done by executing a SET NAMES 'latin1' statement after connecting. The statement can be used regardless of connection method (the mysql client, PHP scripts, and so forth).

    In some cases, it may be possible to configure the connection to use the desired character set some other way. For example, to connect using mysql, you can specify the --default-character-set=latin1 command-line option to achieve the same effect as SET NAMES 'latin1'.

    For more information about configuring client connections, see Section 10.4, “Connection Character Sets and Collations”.

    Note

    If you use ALTER DATABASE to change the database default character set or collation, existing stored routines in the database that use those defaults must be dropped and recreated so that they use the new defaults. (In a stored routine, variables with character data types use the database defaults if the character set or collation are not specified explicitly. See Section 13.1.17, “CREATE PROCEDURE and CREATE FUNCTION Syntax”.)

  • Specify character settings at server startup.  To select a character set and collation at server startup, use the --character-set-server and --collation-server options. For example, to specify the options in an option file, include these lines: 

    [mysqld]
character-set-server=latin1
collation-server=latin1_swedish_ci

    These settings apply server-wide and apply as the defaults for databases created by any application, and for tables created in those databases.

    It is still necessary for applications to configure their connection using SET NAMES or equivalent after they connect, as described previously. You might be tempted to start the server with the --init_connect="SET NAMES 'latin1'" option to cause SET NAMES to be executed automatically for each client that connects. However, this may yield inconsistent results because the init_connect value is not executed for users who have the CONNECTION_ADMIN or SUPER privilege.

  • Specify character settings at MySQL configuration time.  To select a character set and collation if you configure and build MySQL from source, use the DEFAULT_CHARSET and DEFAULT_COLLATION CMake options: 

    cmake . -DDEFAULT_CHARSET=latin1 \
  -DDEFAULT_COLLATION=latin1_swedish_ci

    The resulting server uses latin1 and latin1_swedish_ci as the default for databases and tables and for client connections. It is unnecessary to use --character-set-server and --collation-server to specify those defaults at server startup. It is also unnecessary for applications to configure their connection using SET NAMES or equivalent after they connect to the server.

Regardless of how you configure the MySQL character set for application use, you must also consider the environment within which those applications execute. For example, if you will send statements using UTF-8 text taken from a file that you create in an editor, you should edit the file with the locale of your environment set to UTF-8 so that the file encoding is correct and so that the operating system handles it correctly. If you use the mysql client from within a terminal window, the window must be configured to use UTF-8 or characters may not display properly. For a script that executes in a Web environment, the script must handle character encoding properly for its interaction with the MySQL server, and it must generate pages that correctly indicate the encoding so that browsers know how to display the content of the pages. For example, you can include this <meta> tag within your <head> element: 

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

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Dokument erstellt 26/06/2006, zuletzt geändert 26/10/2018
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