Im pretty new to databases ( ie I have used both Oracle and MYSQL for about 3 months )

My questions is what is the difference in features between Oracle 's latest DB software 10g and MYSQL's latest software 5.0 or 5.1 .

Im just trying to understand why Oracle 10g is still very popular even thus MYSQL is opensource so cheaper. or what is lacking in MYSQL that Oracle has

and also whether their are better opensource alternatives to oracle 10g than MYSQL .

If anyone can answer these questions or knows where I can download/find the relevant info then please reply

Thanks in Advance