There are a number of differences. From my evaluation of MySQL it is missing a number of critical features such as:
Stored Procedure Support
Trigger Support.
For a while it didnt support transactions. They now use something called the InnoDB engine. This provides support for transactions.
Goto
www.mysql.com. They have a ton of information there about current and future versions.
Rod Paddock
Editor in Chief CoDe Magazine
President Dash Point Software, Inc.
VP Red Matrix Technologies,Inc.