SQL type DECIMAL could essentially represent any numeric type. For now Cayenne doesn't have any special treatment for it. It could lead to some minor problems if this type is used.
For instance, PK that is defined like DECIMAL(38,0) would generate Integer value, though it could be treated as Long. And when loaded from the DB it would be set to BigDecimal
We could add some special logic, so it would be more convenient to use.