6.4.2 vs. 6.3.2 - Q's about differences

Hi folks,

Wondering whether by upgrading from 6.3.2 (under RH Linux) to 6.4.2,
I'll get the ability to do unions in subqueries, i.e.:

 select foo from table
    where foo=3 and
    bar in
       (select ... union select ...)

Does this now work?

Also is there any work needed in converting my databases when upgrading?

Finally, the latest Linux RPM I've found for a binary installation is
6.4-5, which I'm assuming isn't 6.4.2 ... any suggestions for the best
RPM to download are much appreciated.

thanks,
Michael