> Damn. That must be the problem, the character set I use for the
> connection is UNICODE_FSS. Does Firebird not allow a table to have
> one VARCHAR column using one character set and another column using
> another character set?

It does.

> If it does allow this, how can this be handled with JDBC if the
> connection character set must match the column character set?

You have to have compatible character sets. NONE is one way compatible
character set other than NONE (I think this is described in FAQ).
OCTETS, for example, is compatible both ways with everything, so you
can do something ugly like this:

SELECT CAST(md5_col AS CHAR(16) CHARACTER SET OCTETS) FROM ...

Or you simply use OCTETS as character set for your MD5 column.

Best regards,
Roman Rokytskyy