I'm not sure what you mean. Do you mean a class for accessing MySQL - lots of people do that - or do you mean a class which accesses any DB which is based on SQL (MSSQL, MySQL, Oracle, PostgreSQL etc)?
If you mean the latter, that's what ADOdb is - a class for any variation on SQL, or at least that's what I understand it to be.
Perhaps I'm missing the point?
Norm