Here is information on how to uninstall APEX. Actually I used it to reinstall APEX due to encountering database errors with a previous installation. After fixing the root cause on database, instead of fixing invalid packages on-by-one, a complete re-installation seems to work more quickly.

1. Shutdown web service

2. Export all workspaces

3. Export application (since I plan not to change the underlying database tables, I do not need to export database data)

4. Drop FLOWS_FILES and all FLOWS_XXXXXX schemas.
to find Schemas may you can use this query, Connect as SYSDBA,
SELECT username from
dba_users WHERE (
username LIKE 'FLOWS_%' OR USERNAME LIKE 'APEX_%')
AND USERNAME NOT IN ( SELECT 'FLOWS_FILES' FROM DUAL UNION SELECT 'APEX_PUBLIC_USER'
FROM DUAL UNION SELECT SCHEMA FROM DBA_REGISTRY WHERE COMP_ID='APEX'
);

and if you want to check what version you have installed APEX, you can with this
query
select version from dba_registry where comp_id='APEX';



5. Re-run apexins.sql from Apex folder with Connect as SYSDBA

6. Import workspaces and then import applications back.

7. Restart web service


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