generic SQL implementations

Has anybody implemented a generic implementation for querying databases during runtime. I am using DAO's for data access layer. But I want to furthur move the database logic to down one more layer of abstraction.I am dealing with different kinds of database (eg. let's say a MySQL, MS Access and another not SQL at all ,index sequential files). I want the DAO to access the database during runtime. So I want my DAO to be independent of the SQL statements.The Database Interfrace would talk to either MySQL,or Oracle or any other database.So that there is no need to have DAO for each database syntax, rather , this should be handled by a API thru an interface.

Here's and examples

Let's say for select statement , we supply table name, column names, where cluase , and's etc

The following method should handle the query

List getSelect(String tablename, List columnnames, List Orderby,.....) etc {

return queryresult
}

Any ideas appreciated
Thank you
Vinay