The @formula annotation should warn to use the samples it gives as this makes your application database dependent.

The @formula annotation javadoc contains a sample containing a string function "substring" that does not work on oracle. Oracle supports "substr". The javadoc for @formula should contain a hint that these sql expressions always are database dependent and there is no way to configure a database dependent sql expression per database to use "substring" on mssql and "substr" on oracle. (right?)