Upgrading from 12.5.0.3 to 12.5.4 or later modifies syscharsets. All of the sort orders that were (formerly) destined for use with unichar was rewritten in terms of ID and CSID, although the names remain the same. Other sort orders (that is, any that you loaded with the charset utility or the sqlloc GUI front end) remain unmodified.
While running under 12.5.4, you may configure UTF-8 with a non-binary sort order. If you return to 12.5.0.3 that server fails to start, with a message saying that the character set/sort order combination is not supported. Versions earlier than 12.5.0.3, however, do not have the error handling code; you do not get the message but instead see inexplicable behavior. The most likely symptom is that the server cannot find anything using indexes on the system tables.
To get around this:
Restart the 12.5.4 server.
Configure UTF-8 with binary sort order bin_utf8 (ID 50). Do not use any other binary sort order (there are three to choose from); bin_utf8 is the only one known to 12.5.0.3 and earlier servers.
Now when you start 12.5.0.3, syscharsets is still in the 12.5.4 state. If you run sp_helpsort, rewrite syscharsets to a close approximation of what it was before the upgrade.
If you execute sp_helpsort now,
and then decide to go back to 12.5.4, be aware that although syscharsets is
in the 12.5.0.3 state, the upgrade does not run again since it has
already run once. Execute sp_helpsort again
on return to 12.5.4 to update the syscharsets table.
