Alter Pluggable Database Open – (ORA-00604/ORA-01405) After Apex Installation

While trying to open one pluggable database, I got the following errors:

Background:

While installing Apex 20.1 in one PDB, and while being very close to the installation completion, the session fully stucked.
I restarted the database (the CDB), then I tried to open the PDB, but I got the above errors.

While searching for this error, I came to very similar issue:
https://wikidba.com/2020/02/09/alter-pluggable-database-fails-with-ora-00604-ora-00001-unique-constraint-sys-i_pdb_alert1-violated-ora-1405-fetched-column-value-is-null/

Analysis:

Initially,I started the database in “upgrade” mode, then I checked the status of the installed components:

As you see from the above output, the Apex’s version is NULL. This is due to the in-completed Apex installation.
(Note that the above errors are not Apex-specific, and may happen with any other components).

Solution:

First, we will de-install the Apex, while the PDB is in the upgrade mode:

Now, run the above query again, and ensure Apex is not there:

The last step is to close the PDB and open it again in the normal read write mode:

The PDB started normally without the above errors.
Now, I can proceed with the Apex installation again, as explained in my post:
https://ahmedfattah.com/2020/05/02/oracle-apex-20-1-installation/

Thanks
Ahmed