You can encounter compatibility issues between different releases of Oracle Database that may affect your applications.
Compatibility issues can occur due to differences between Oracle Database releases. Also, in each new release of Oracle Database, new Oracle reserved words can be added, or initialization parameters can be changed, or the data dictionary can be changed. Review the relevant topics in this documentation for more information.
When you upgrade your Oracle Database software to a new release, ensure that your applications do not use any Oracle reserved words, that your applications are compatible with the initialization parameters of the database, and that your applications are compatible with the data dictionary of the database.
Also be aware that new releases of Oracle Database may be supported only on particular operating system releases or patch sets. An operating system release and patch set that is supported for use with a previous release of Oracle Database may not be supported for current releases. Check operating system requirements before you begin an upgrade. In addition, some features may require additional patch sets or kernel additions to be able to use.