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. The range of IDs from 1024 to 2047 is reserved for user-defined collations. The collation ID that you choose will appear 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:

mysql> SELECT MAX(ID) FROM INFORMATION_SCHEMA.COLLATIONS;
+---------+
| MAX(ID) |
+---------+
| 210 |
+---------+

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

mysql> SELECT ID FROM INFORMATION_SCHEMA.COLLATIONS ORDER BY ID;
+-----+
| ID |
+-----+
| 1 |
| 2 |
| ... |
| 52 |
| 53 |
| 57 |
| 58 |
| ... |
| 98 |
| 99 |
| 128 |
| 129 |
| ... |
| 210 |
+-----+

Warning

Before MariaDB 5.5, which provides for a range of user-defined collation IDs, you must choose an ID in the range from 1 to 254. In this case, if you upgrade MySQL, you may find that the collation ID you choose has been assigned to a collation included in the new MariaDB distribution. In this case, you will need to choose a new value for your own collation.

In addition, before upgrading, you should save the configuration files that you change. If you upgrade in place, the process will replace the your modified files.

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