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 will appear in these contexts:
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 | +-----+
Before MySQL 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 MySQL 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.