What about upgrading from older versions of MySQL? MySQL 4.1 is almost upward compatible with MySQL 4.0 and earlier for the simple reason that almost all the features are new, so there is nothing in earlier versions to conflict with. However, there are some differences and a few things to be aware of.

It is important to note that the “MySQL 4.0 character set” contains both character set and collation information in one single entity. Beginning in MySQL 4.1, character sets and collations are separate entities. Though each collation corresponds to a particular character set, the two are not bundled together.

There is a special treatment of national character sets in MySQL 4.1. NCHAR is not the same as CHAR, and N'...' literals are not the same as '...' literals.

Finally, there is a different file format for storing information about character sets and collations. Make sure that you have reinstalled the /share/mysql/charsets/ directory containing the new configuration files.

If you want to start mysqld from a 4.1.x distribution with data created by MySQL 4.0, you should start the server with the same character set and collation. In this case, you won't need to reindex your data.

There are two ways to do so:

shell> ./configure --with-charset=... --with-collation=...
shell> ./mysqld --default-character-set=... --default-collation=...

If you used mysqld with, for example, the MySQL 4.0 danish character set, you should use the latin1 character set and the latin1_danish_ci collation:

shell> ./configure --with-charset=latin1 \
           --with-collation=latin1_danish_ci
shell> ./mysqld --default-character-set=latin1 \
           --default-collation=latin1_danish_ci

Use the table shown in Section 9.1.11.1, “4.0 Character Sets and Corresponding 4.1 Character Set/Collation Pairs”, to find old 4.0 character set names and their 4.1 character set/collation pair equivalents.

If you have non-latin1 data stored in a 4.0 latin1 table and want to convert the table column definitions to reflect the actual character set of the data, use the instructions in Section 9.1.11.2, “Converting 4.0 Character Columns to 4.1 Format”.