It's highly unlikely you could ever use generic enough SQL to go from open source DB or Oracle. Best case you wouldn't be getting the best performance out of y

It's highly unlikely you could ever use generic enough SQL to go from open source DB or Oracle. Best case you wouldn't be getting the best performance out of your open source database and then you wouldn't be getting the best performance out of Oracle. It's better to build for the platform you have than build for a mythical common platform that contains the minimum features of syntax of all of other DBMS (which probably doesn't exist). If you change DB platforms, you're just going to have to rebuild.