I am currently using MySQL 3.23 for a live web site. I have new
queries that need UNION provided in v4.0.0+. It's a simple db with 5
tables and doesn't perform any e-commerce type transactions. All of
the 7 tables are of type MyISAM. So I have to upgrade MySQL on the
live server.

Q: Do I install to 4.0.12, or 4.1, or 5.x ? Because the application
is simple - is version 5 safe? My guess is that the core of the
server engine would be much the same for simpistic queries?

What are other people experience and thoughts on this? I understand
that safest would be version 4, then 4.1, then 5 - however it would be
nice to have 4.1's ability to do subqueries and derived tables.

Thanks in advance - Will