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10.3.3 Database Character Set and Collation

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Every database has a database character set and a database collation. The CREATE DATABASE and ALTER DATABASE statements have optional clauses for specifying the database character set and collation:

  1. CREATE DATABASE db_name
  2.     [[DEFAULT] CHARACTER SET charset_name]
  3.     [[DEFAULT] COLLATE collation_name]
  4.  
  5. ALTER DATABASE db_name
  6.     [[DEFAULT] CHARACTER SET charset_name]
  7.     [[DEFAULT] COLLATE collation_name]

The keyword SCHEMA can be used instead of DATABASE.

The CHARACTER SET and COLLATE clauses make it possible to create databases with different character sets and collations on the same MySQL server.

Database options are stored in the data dictionary and can be examined by checking the INFORMATION_SCHEMA.SCHEMATA table.

Example:

  1. CREATE DATABASE db_name CHARACTER SET latin1 COLLATE latin1_swedish_ci;

MySQL chooses the database character set and database collation in the following manner:

  • If both CHARACTER SET charset_name and COLLATE collation_name are specified, character set charset_name and collation collation_name are used.

  • If CHARACTER SET charset_name is specified without COLLATE, character set charset_name and its default collation are used. To see the default collation for each character set, use the SHOW CHARACTER SET statement or query the INFORMATION_SCHEMA CHARACTER_SETS table.

  • If COLLATE collation_name is specified without CHARACTER SET, the character set associated with collation_name and collation collation_name are used.

  • Otherwise (neither CHARACTER SET nor COLLATE is specified), the server character set and server collation are used.

The character set and collation for the default database can be determined from the values of the character_set_database and collation_database system variables. The server sets these variables whenever the default database changes. If there is no default database, the variables have the same value as the corresponding server-level system variables, character_set_server and collation_server.

To see the default character set and collation for a given database, use these statements:

  1. USE db_name;
  2. SELECT @@character_set_database, @@collation_database;

Alternatively, to display the values without changing the default database:

  1. SELECT DEFAULT_CHARACTER_SET_NAME, DEFAULT_COLLATION_NAME
  2. FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = 'db_name';

The database character set and collation affect these aspects of server operation:

  • For CREATE TABLE statements, the database character set and collation are used as default values for table definitions if the table character set and collation are not specified. To override this, provide explicit CHARACTER SET and COLLATE table options.

  • For LOAD DATA statements that include no CHARACTER SET clause, the server uses the character set indicated by the character_set_database system variable to interpret the information in the file. To override this, provide an explicit CHARACTER SET clause.

  • For stored routines (procedures and functions), the database character set and collation in effect at routine creation time are used as the character set and collation of character data parameters for which the declaration includes no CHARACTER SET or a COLLATE attribute. To override this, provide CHARACTER SET and COLLATE explicitly.


Rechercher dans le manuel MySQL

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Document créé le 26/06/2006, dernière modification le 26/10/2018
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