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12.14.2 Choosing a Collation ID

Each collation must have a unique ID. To add a collation, you must choose an ID value that is not currently used. MySQL supports two-byte collation IDs. The range of IDs from 1024 to 2047 is reserved for user-defined collations.

The collation ID that you choose appears in these contexts:

  • The ID column of the Information Schema COLLATIONS table.

  • The Id column of SHOW COLLATION output.

  • The charsetnr member of the MYSQL_FIELD C API data structure.

  • The number member of the MY_CHARSET_INFO data structure returned by the mysql_get_character_set_info() C API function.

To determine the largest currently used ID, issue the following statement:

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mysql> SELECT MAX(ID) FROM INFORMATION_SCHEMA.COLLATIONS; +---------+ | MAX(ID) | +---------+ | 247 | +---------+

To display a list of all currently used IDs, issue this statement:

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mysql> SELECT ID FROM INFORMATION_SCHEMA.COLLATIONS ORDER BY ID; +-----+ | ID | +-----+ | 1 | | 2 | | ... | | 52 | | 53 | | 57 | | 58 | | ... | | 98 | | 99 | | 128 | | 129 | | ... | | 247 | +-----+
Warning

Before upgrading, you should save the configuration files that you change. If you upgrade in place, the process replaces the modified files.