> This query is not good for Firebird...
> I can see problems in 2 diferent points:
> 1.
> select ... from (select

Yup, you're right - this is not supported in Firebird 1.5. It works ok in
Firebird 2.0, I was able to pass Hibernate's test suite with slightly
modified FirebirdDialect and Firebird 2.0 post-alpha3 snapshot. Anyway, that
is not for production use, but I'm tracking this relatively close. However,
Fyracle might be an option for you, since that is FB 1.5.1 + backports of
some FB2 features (for example "select from select").

Roman