Review this information if you use multitenant architecture, and after the upgrade, you want to plug in a PDB that contains Oracle Application Express releases 5.0.0, 5.0.1, or 5.0.2.

Oracle Database 12c release 2 (12.2) includes Oracle Application Express release 5.0.3. The Oracle Application Express versions can be incompatible. Incompatible versions are an issue when you upgrade Oracle Database release 12.2, you plug in PDBs that contains earlier releases of Oracle Application Express, and then upgrade to Oracle Application Express releases 5.0.0, 5.0.1, or 5.0.2. If the Oracle Application Express versions are incompatible, then when the PDB is upgraded, the Oracle Application Express release on the PDBs is not patched to release 5.0.3. In that event, you can only use it with restrictions.

To complete the upgrade of Oracle Application Express to release 5.0.3, you must carry out a procedure to run an additional package. Refer to the section "Working with Incompatible Application Express Versions" in Oracle Application Express Installation Guide. Complete the required actions so that you can plug in PDBs with earlier release Oracle Application Express installations.